re: What should I say to my white brother-in-law that thinks he’s black?

Your wife's brother? Ahh. I gotcha. So he is disrespectful to your inlaws. That makes sense why you would be pissed. That changes things a little bit.

You should just have another talk with him and tell him that he really needs to get his shite together because he has no clue how good he has it. 20-30 years from now or whenever his parents are no longer around, he will look back and think about how shitty of a son he was to them so he needs to start being more appreciative of them now.

What does your wife say about the situation?