In all seriousness if I was concerned that a skid was going to go all axe murderer on me I’d be doing more than putting a lock on my door. I’d get the hell out of there. Use your own judgement I suppose on the likelihood...

read my posts when it comes to an upredictable maliscious SS12.   I would be concerned ,,, what about his father and what does he say about it ?  I would moniter this very carefully 

Ok... so my SS20 is Autistic and mentally closer to a 12 yr old. He talks about Star Wars all the freaking time... like obsessed. He will say random things about nuclear bombs or death star or EMP's or whatever- to him it is "cool" like watching big explosions in action movies are "cool" to see. It is those action scenes in his head that are fascinating to him. He doesn't actually want to have real people die but fantasy and reality are very blurred for him when it comes to that kind of thing. 

I wonder... if there isn't something more going on here. The fact that he has tantrums at 12, rude (no brain to mouth filter), immature, talking about fantasy as if it is real (death star), hates people... That is all too familiar to me. My stepson would happily live on the moon if he didn't have to see people. That is Autism. 

ETA: There is a really huge spectrum. There are people you wouldn't even realize have Autism because they function in the real world- go to college, have normal jobs, etc. BUT they are different in their processing of the world around them. Many go undiagnosed until their 20's. It wouldn't hurt to have him go through an assessment. If for no other reason than it can change the way you perceive him and how you address things like this. Having a SS who is Autistic and won't likely ever live on his own, I can say that I have learned a lot of grace and how to let things go. It makes a difference in my behavior and my expectations of him. I am better at knowing what his limits will be and not not push him too far. What social situation he is ok with and even what guidelines we have for him on situations that he isn't happy with but has to go to anyway. (For example a wedding for his Aunt. No phone in the church. He has to sit at the table with us until after food is served. He had to respond when people talk to him. Then he can go find a place to sit alone for the remainder of the wedding)

my SS 14 finally agreed to see his father after not seeing him for 2.5 years. First thing my SS said when he arrived was " did you know that guns were made to kill people" and then in normal conversation, you know if I wanted you gone you would be, its easy.  Needless to say the week he was here I stayed away from him and watched my back the entire time. Before he left, he said, oh ill be back and maybe to move in when I'm 18. WATCH YOUR BACK!

yes be careful!!!! my exSS13 would damage my belongings with knives,, once he took an axe from the shed and angrily hacked the whole side of a tree out that happened to have a love heart with mine and his fathers names carved in it when we moved into the property.  I caught him once kicking the dogs legs out from under him as he walked by.  All i can say is it got extremely worse and I had to end the relationship .  PLesae be careful and maybe put little cameras around just encase , i wish i did !!!