Your brother-in-law’s jokes don’t really sound like jokes. You know it. I know it. He knows it. If they were actually jokes he’d pick on you about something you have a big ego about, or something ridiculous and innocuous, not all the places you are most vulnerable. They only become jokes when you call him out on it, like, if you said “Hey, that nickname really hurts my feelings, please stop using it” or “I am confused by your comments about how I am not doing anything useful; I’m studying.” Then they will become jokes, he was just joking, his hands will go up, and he’ll back away from you because you’re so “sensitive” and “serious” and “you can’t take a joke.”
This dynamic is dismayingly common.