My brother in law is not really well liked by most people. He's moody and doesn't like to have fun. He has done and said things over the years that have pissed everyone in my family off. He used to have intense blow outs with my mother and in one case he even threatened her with physical violence. But after 12 years of being married to my sister, we have all just learned to live with him for her sake. I probably know him better than anyone else in the family due to how much time I spend with my sister and their kids. And for a while it seemed like things were good between us. We finally had an understanding of one another and he really seemed to like me. But, as usual when it comes to him, that only lasted so long.

Things started getting shitty a few months ago when I was over their house. I went to use their ice maker to get a drink, and he mumbled "Could you be any FUCKING louder?". This is the type of shit he does. It's like he wants to alienate you and make you feel totally uncomfortable. Anyway, I ignored it because fighting with him is not going to do anything but make my sister feel uncomfortable and I also have manners, so fighting with someone in their own house is not something I do.

My sister and I have decided to go into business together, working off of a brand that I have already established and worked hard to make a success. I brought her into it and we work really well together. We are still in the stages of product development (which takes TIME). One night a few weeks ago my brother in law walked in as we were working, looks at me and says "Still haven't put anything up for sale yet, huh? Well I see YOU really made out on this deal" and then walked away. I was fucking furious. What the fuck does that even mean? Do you think I'm secretly profiting off of my sisters hard work? Fuck you!

Things have just gotten even worse. He's always making shitty comments and acts like a raging asshole whenever I'm around. I don't understand him at all. I'm good to his kids, I'm best friends with his wife, I even cook for him on occasion! I don't know why he wants me to feel so uncomfortable around him. My sister asked me last week why I act so timid around him and I said "cause he's mean to me!". She tried to play it off like he's just joking around with me but she doesn't even know some of the stuff he's said because I don't want to put her in a crappy position.

To make matters FAR worse, I think he is a terrible parent to my niece (who is my FAVORITEST PERSON IN THE WORLD). He is borderline abusive toward her. Or, maybe even totally abusive but I'm trying hard not to think that way because it breaks my fucking heart. And my sister is scared of him, although she'd never admit it. He's just such a fucking asshole and it's getting to a point where I don't know how much longer I can keep letting him treat me like garbage. His temper worries me and gives me anxiety.

What do I do? I am trying so hard to lay low around him and be nice and it's met with all this weird snide hostility. I don't want to have to get my sister involved because that feels really unfair. But shit! He's a douche! Any advice or similar situations you can tell me about?