I Need To Fight Back?

Alright this kid has been a jerk he makes fun of retarded kids to their face he picks on tiny kids and i have personally been verbaly telling him to stop and i never thought of physically hurting him but i got surgery abut a week ago and whenever ive been around hes been trying to pick on me he even punched my girlfriend in the face and hes still making fun of the people he used to and he even tried hitting me im a boxer and martial artist and i know i can hurt him in self defense but i dont know if i should fight back or not