My boyfriend's good brother makes fun of me at will.

Why don't you ask your boyfriend to solemnly warn him that you can joke but not my girlfriend? What your boyfriend's good brother said shows that he doesn't respect you, understands your hurt feelings, and has a serious talk with your boyfriend! Tell your boyfriend to either warn that person to shut up, or break up with that person or break up with you. Let him choose one. By the way, you can test how much your boyfriend values you.