I would suggest trying to differentiate between whether they are making fun of you because you guys are close. And it’s just a sign that these are your good, intimate friends. OR They are putting you down to actually hurt your self esteem long term, and discourage you from improving in life. There is a difference. Sometimes even our good friends knock each other down just for fun. Especially guys do this as a form of bonding. It’s kinda like after a professional sports game, the player that performed the best might get a container of Gaterade poured on them from their teammates. It’s not an attempt to bully, it’s a type of bonding. But if it is the latter, and they are actually trying to put you down long term, then you might wanna go it alone for a little while without friends. Either way, you can be honest and tell them it hurts your feelings when they make fun of your stuttering and go from there.