If someone is making fun of you, you have to clap back. Hit him back with some spicy words that will hopefully cut deep enough so that he know not to mess with you. To do this properly you have to find his weakness. Find out what he is insecure about and then call it out so he knows that this thing he was worried about is actually something people actively think about. If it works properly he will cry on the spot and maybe even pee himself.