Why have you tolerated this for four years? Has this been a discussion you and your spouse have had about SS moving out at some point? I have a feeling your wife is a Disney Parent and you are trying to get around admitting that.

Have you talked to your wife about an "exit plan" for her son.  4 years is enough time for him to get his act together.  At this point, it likely would be preferable for him to move out.. even if mommy had to help him a bit ito make ends meet.  But, I'm guessing the fact that you have him living on your couch in your living room means you and your wife probably don't have the means to do that for him... in an effort to get him to spread his wings.

It is way past the point for you and her to have a conversation about how long this has been going on.. and what steps he needs to take to get off the couch and out of the home.  I would be inclined to take his key away and not allow him to remain in the home for certain hours of the day.. like 8 am to 6 pm.. those are lockout hours.. you can sit and watch your phone.. but you can't do it here.  go to the library.. the park.. or maybe get a job to fill your time.

start charging rent.. and groceries.

Give him a deadline.. 6 months and out.. he may not be able to afford his own place.. but he can find a roomate situation... and there ARE jobs out there.. maybe not in restaruants.. but there are jobs.. 

Dumb Sh!t.

Sorry. I know thats tough to read. But you wife has been enabling DA to the point of disabling him and as such she deserves a big part of the blame, at least in the first few years 1-2. He is an adult that has been allowed to not progress. ALLOWED by DS. But now its on him (yers 2-4).

I know this because we have SD21 Feral Forger, who has been living with BM Toxic Troll. Im 6 plus years in this, and it wont change unless your wife DS, operates some tough love. And Im not talking anout tidying the futon tough love. He needs a drivers license. He needs a full time job. Start charging him rent - if he can afford beer then he can afford 100/monthly. Who pays for his food btw? Dont tell me your wife cooks and feeds this cretin! 

SD21, also has no job and no license and was party hardy until a few weeks ago. Apparently she just started college courses. And has been cleaning her area. But she will never be living in MY home ever again. DH knows this. You need to be very tough on your wife, so she can put more pressure on DA.

He needs to be given a hard deadline.  He does sound depressed to me but sitting around sleeping, drinking and playing video games is not going to help with that at all.

Sad to say you are a step parent whatever his age. That situation sounds intolerable. My adult daughter lives with me but she a seperate section of the house.

He isn't going to launch on his own. A definite plan needs to be made even if that means you and DW take the initiative.

At this point since he seems to have low standards, I would search for cheap rooms for rent, pay the deposit  and drop him off with the agreement he can not come back. Change the locks and stick to it. 

I would also let DW know if he comes back you are leaving.

I have had to already have this conversation with SO. I can predict his kids will not launch. Do to the serious lack of parenting, they will never have the social skills to adult. I have made it abundantly clear to SO they are not living here once they are adults. 

Unfortunately I feel bad because I predict they will end up mooching off Thier grandparents, but I refuse to be responsible for adult kids. I have plans to have a life once I retire and travel, not raise dysfunctional adults. It's not my fault they are the way they are, I had nothing to do with raising them. I will not suffer the consequences of Thier failures in life. 

Time for him to leave. If he was my son or daughter I would not stand for this crap AT ALL.

As I've learnt here very recently, it's not the kids fault, it's the parenting. There is no waw ANY child should be allowed to behave like this. Sort the mum out, you need to have some serious words with her and it also looks like you need to find yourself another place.

Maybe the Burning Platform isn't the right approach, but maybe a smoldering one could work.

DumbAss has no REASON to do anything other than sit on the couch. His mother has no expectations of him. How about adding in one daily chore, so it's a slow build up to developing life skills? How about you give him a list of seven things that must be accomplished over the course of a week? Clean the bathroom, scrub the kitchen floor, weed the garden, whatever. And one thing must be done each day, otherwise no internet the next day. Build into his chores various life skills -- developing a budget, cooking a meal, paying bills.  After a time make one of his chores compiling a list of other places to live.

All the other stuff is good but don't let the animals suffer until he shows he can be relied on

This is not complicated.  You need to light a burning platform under his useless ass and force him to leave.

We had to do this with my SS-28 when he was 18.  He graduated from HS at 17 so we let him have the summer after graduation on our dime.  Getting him out of HS was a challenge. He used to abhor being the center of attention so he would rest comfortably at the middle of the pack where he could be easily ignored.  To deal with his severe underperformance we sent him to Military School for his Jr. and Sr. year of HS... at least that was the plan.  He kicked ass his Jr. year. Honor Student, Military Leader recognition, recognition for his athletic performance and his performance in the Band. He lost 40Lbs the first 6 weeks of his Jr. year and went from a doughy boy to a rock hard fit young man of confidence.  Then... his Spermidiot helped him hack the school fire wall at the beginning of his Sr. year for them to stay up all night playing WoW together so he was comatose in class, and he caught Swine Flu.  He was in the infirmary for three weeks.  His teachers would bring all of his work to the infirmary and he did none of it.  He failed the only class he needed credit for during the first semester of his Sr. year in order to graduate. He failed all but one class.  The one class he needed for graduation (Sr. Eng. 1) was not offered during the Spring nor over the summer so we would have had to pay for two more semesters just to get him a diploma from his top 20 in the nation boarding school.  My wife said hell no and yanked his ass home at Christmas break where she scared the shit out of that kid.  He had one semester to get his shit together and graduate or he was out.  Tax season slams her professionally in mid Jan through mid June every year so he and I had a ton of time together for me to give him the continual come to Jesus lectures on how bad he screwed up.  One Saturday while his mom was slamming out Tax returns I loaded him up for a drive to Philly and dropped him off at the homeless camp under the elevated Interstate.  Then I drove off.  He did not know it but I pulled into a shopping center a couple of blocks away and circled back behind the shopping center and parked behind a dumpster where I could see him.  And I sat there and watched him for about 2 hours.  Those homeless folks were incredible.  They fed him, gave him hot coffee, hugged him, scared the ever living shit out of him, lectured him about how good he has it and how he needed to pull his head out of his ass, etc.....  When I pulled up, rolled down my window, and told him to get his ass in the car it was obvious he had been sobbing on and off for most of those 2 hours.  As he walked away from the homeless camp I got several winks and thumbs up from those Angels.  On the drive home I told him June 2nd we either went to his HS graduation or we would be dropping him off at the homeless camp with a Walmart pup tent, a sleeping bag, a new coat, new shoes and a fast food gift card that would feed him for a month.

For the next 5mos that kid was nothing but books, studying, assholes and elbows with his nose to the grind stone. He graduated on time and with honors from our local HS.  If he had kept his head in the game at Military School he would have only needed to take a few classes in the Spring and would have needed only Sr. Eng. 2 to graduate.  At our local HS he needed Sr. Eng. 1&2, two math classes, two career track classes (He cataloged and computerized the entire music library for the school music program), and he had to finish a Sr. project that was assigned at the beginning of the Spring semester of Jr. year. He only had 5 weeks to get a uear and a half project complete. That kid busted his ass.  That whole semester he would occassionally plop down on the sofa next to me and say "Dad, I screwed up. Mom is so mad at me."  Tears would just flow down his cheeks. No sobbing, but he was feeling the gravity of his choices. I would just tell him "Yep, you screwed up and your mom is mad at you. But mostly she is hurt and she is afraid for your future.  So am I."  I would but my arm around his shouders for a few minutes then send him back to his books.

Then we moved.  He came with us.  The day after he graduated he and I left and drove for three days where I dropped him off at my parent's house.  He spent the summer with us, visiting my parents and going on an RV trip with mom and dad and his boy cousins, he visited SpermLand for a few weeks, then he came home.  He turned 18 while he was visiting SpermLand.  To make sure he would not tell us he was staying in SpermLand and wasting his life with the shallow and polluted half of his gene pool  my wife and taken a road trip with her brother (my BIL2) from Houston to Oregon to be there on the day he was supposed to end his finaly COd visitation.  I flew up a couple of days after she picked him up and we had a nice family road trip back to Houston.  As was usual after a SpermLand visitation he was sullen and withdrawn for the first couple of days but started to engage as the trip progressed.  The N. rim of the Grand Canyon was what finally drew him out of the post visitation detox period.  It was a nice trip. We re-established our 3 Musketeers relationship.  Then the day after we got home, we smacked him in the face with real life.  We had offerred him the mom and dad full meal deal full ride college scholarship to any school he wanted to go to (that would accept him).  His Military School had offered him a JC scholarship and the Army had offered him a slot in their early commissioning program.  But... he failed out and all of that went bye bye.

I am actually very proud of how he handled the topic of college. During our post visitation road trip he finally told us "I am not ready to focus and put in the work I need to invest to be successful in college.  I know finishing my degree is important and I will finish it but right now it would be a waste of my time and your money."  Certainly not what we wanted to hear ... but.... he knew where he was at and he stood his ground.  We made it clear that he could stay in the family home rent free if he was either a full time student or working full time. Or half time student and working part time.  Nope, he was not interested in a job.

So.... we turned him into our live in beck and call boy/chore bitch.  We worked that kids ass off.  His mom went CPA spreadsheet chore list on his ass.   For the next 8mos that kid scrubbed, cleaned, swept, vacuumed, mopped, dusted, polished, washed, dried, folded, put away, weeded, trimmed, mulched, mowed, painted, brushed cobwebs off of the outside brick walls, sliced, diced, chopped, cut, roasted, fried, mashed, baked, prepped, cooked, served, then cleaned it all up. If he got the days chores done, he could stay and do the next day's chores. If he didn't get all of that day's chores done, he was out the next AM when his mom and I lefr for work. No money, no food, just the garden hose for water. Which was a funny story.

We would drive off with him standing on the front step of the house with a forelorn look on his face.  He only tested us twice.  Once when it was over 100*F outside and a second time that Winter when it was in the low 40s.  When we got home from work on the hot day he spent locked out of the house he was lying prostrate on the back patio totally parched. When I opened the back door to check on him he was so mad.  "Dad, I did not have any water and it was HOT!"  That is when I pointed to the garden hose and said... you had plenty of water son. Next time, finish your chores and you won't have to suck on the garden hose to get a drink.  The second time he tested us, we left him on the front stoop in his sleep pants and a T-shirt and flip flops. I tossed him the blanket off of his bed as I locked the front door.  He was uncomfortably cold when we got home that evening. But... he got to work on his chores and made sure they were done before we left for work the next AM.

After 8mos of being our beck and call boy/chore bitch, we dropped him off at MEPS to ship out for USAF BMT.  Two months from tomorrow will be his 10 year service date in the USAF.  His 6 year re-enlistment papers are in process now.  He has completed an AS in Computer Science and is working on finishing he BSCS.  Slower than his mom and I would like, but he has been true to his word and is working on it.

His mom and I are very proud of the man we raised together.  I became his dad when his mom married me the week before he turned 2yo.  When he was 22 he asked me to adopt him. We made that happen.

A key to the success of our burning platform model with getting SS to launch was that we turned off the internet and cable TV when we left the house each AM.  Our house had the SmartHouse system and all of the control of the system was in our MBR closet behind a locked panel.  He could watch whatever we were watching in the evening after he finished cleaning up after dinner and he could use the internet until we left for work the next AM.  But he was digitally dark from the time we left for work until we got home from work.  He was on our cell plan and knew that we could make that go away too.

Try it, load up the router and the cable box every AM when you leave for work. To make a point, get a rugged locable cabinet to lock them in before you leave.  Or, put them in the trunk of your car before you drive off.  Give him the chore list to have done by the time you get home from work. If he does not do it, leave him on the front stoop until you or his mom get home from work.  Rekey the locks and don't give him a key.   Start handing him brochures for the US Army, USMC, USAF, Navy, and Coast Guard every couple of weeks.  Between being your chore bitch, having zero internet and TV, and if he is on your phone plan have his phone service cut during work hours, and the building life of abject misery he will experience he will launch.

This is not his dad's fault.  He is not milking his dad for his shelter, food and digital entertainment. You are your DW are the suckers he is playing.  BTW, decent people do not do what this POS failed family spawn is doing.  Get it out of your head that he is a decent person. He isn't. His choices and behavior proves it.

Grow some balls man.  Solve the problem.  Start by taking your bride out for a nice dinner and laying out the plan.  Tell her it is happening and you hope she participates but that it is happening whether or not she participates. My wife was completely on board. Much of it was her idea.  She was the one that sat him down at Christmas of his Sr. year and gave him the come to Jesus talk that he was not returning to Military School.  She went all CPA on his ass. She had a presentation packet, spreadsheets showing what his schooling had cost us, and what he lost out on because he made the stupid decision to let the Spermidiot pollute his opportunity.

My son knew better than to throw tantrums, or to be disrespectful.  He did test us, but he was very measured in how far he pushed.  He was an adult, so we treated him as an adult.  Adults work, they contribute, and they feel the pain of their failures.  Our job was to bring the pain.

Your job is to bring the pain.

So do it.

Put a hand between your legs, grab a big handfull of man sack, and man up.  

I forecast great things for your marriage and even for your Skid if you do.

Good luck.