I had a teenage female in the house who was a nightmare and several of her dad's friends told him.....when two males are fighting over territory, one pisses all over everything to mark his own.....when there are two females....one tries to push the other one out. In my case, I left of my own free will with what little sanity I had left. It does not get better and as long as your wife enables this, it will continue to get worse. You are questioning yourself the same as I did, that maybe there is/was something wrong with you/me. I don't think there is anything wrong with you. In your case it isn't about having another male in the home, its about having another "body" in the home that refuses to contribute. I venture to guess that you would have these feelings whether the other body was male or female. You have legitimate gripes and concerns.

It is hard having another person in the house, I agree with the above. Its kinda like this:
If two women lived together it would be just as hard because the kitchen only has room for one women,
See what I am saying?
Women have different ideas about how to make their home and what they like and how they want it, from colors to furniture to whatever, 2 women are more then unlikely going to agree with a style at a 100%,
So is it with men and their tools and garage, Just like women their favorite space and things are just so and organized in such away and had better stay that way, No what I mean?
And then there is the whole aspect of the lable called:
" The man of the house",
Your SS is older now, and he is at that age where they feel dominate, their finding their male ego of persona and space " No doubt", My son is 14 and trys to pull it all day long, And I keep reminding him I am the adult, he is the child, I pay the bills ...
Lives under my roof and when he is 18 and wants to do whatever then fine, But he is not the boss no matter how old he is while living under my roof.The whole additude of boys becoming young men is different then girls,Theirs is all about the male ego.
And unfortunatly like all teenagers they think the world owes them everything, and they know everything and well.. you just don't know things like they do, Its the age and it comes with no life exsperience at all, We all have went through it sometime or another as children. Its part of growing.. think back to when you was his age and maybe you can kinda put a little more perspective to how you feel and whats going on with him.

Amen to the last post. Its not just steppies tho. My bio troll age 18 just moved out (she is two months from graduating high school) because she said that she is 18, can do what she wants when she wants eyc and I cant do or say anything baout it. After I picked my laughing butt up off the floor I told her that is not how a HOME works. She went upstairs, packed her things and was moved out that night. She left saying there is no on going to tell her where she can go, with whom, what time to be home etc and if she doesnt want to work she doesnt have to.
Its hard but because she is 18 I could not stop her. Its a tough lesson but usually from my experience that the tougher the lesson the greater the learning.
I have a 22 year old that has been living at home since she left college two years ago. She is a hard worker, shares the bills, helps around the house etc. Thankfully I havent had to piss on anything to mark my territory...lol We have gotten on each ithers nerves and a fewlines have been crossed but her respect gets back in line as quickly as it went out.
I dont know about how it is with guys as I havent had any sons in the house. But i am sure there is tension on both sides. The son wants to be grown up, the dad wants him to be grown up but they see the meaning of "grown up" as two different entities.