I hate my F-ing In Laws

[Ghaleon]

There is literally no upside to you beating the shit out of him,

Except that it will make me feel really really really good. And honestly, after he got raunchy with my wife (sister or not), I feel I'm making an enormous concession by allowing him to keep all of his teeth.

Basically you can:

1) clench your teeth and deal, and count the minutes till the guy leaves town... like pretty much 99% of people would do in a situation like this

2) talk to the guy about it, without getting all pissed off, and just make it clear that what he did was too much and won't be tolerated in the future. this won't work without you apologizing for vaguely threatening to kill him however..

1) No dice. this is where I think I need to tell mroe of the story, but it's really long and I doubt anyone here REALLY cares. But the cliffs notes are a) he treats his mother like absolute dog sh-t, even in public.
b) He has no sense of how to be a respectful houseguest. I shouldn't find him at noon, on my couch, with his boxers around his knees, his ass exposed, and his face buried in a cushion soaked in his drool while the bed with clean sheets that I provided for him goes unused.
c) He says hateful and hurtful things TO my kids. He didn't like the way my 9 year old was acting on a family vacation one time so he got in her face and told her that he would buy presents for her sisters, but not her. The kid was devastated.

2) Oh we will have a talk. I am going to make sure that there is no question in his mind about what the expectations are. a) He is going to refrain from drinking, smoking, yelling, swearing, burping, farting, or even sneezing around my kids. b)He is going to treat his mother, my wife, and my daughters like queens. c) he is going to sleep in a bedroom, and he is going to keep it tidy. There's probably more, but that's a good start.

the best outcome for you would be that this dude does get his life together .

Completely disagree. The best outcome for me would be if a piano falls on his head.