Don’t forget also that since the professor did this he is showing all the it’s okay to laugh at you. It’s disgusting, report him or at least have a long conversation with him about it one on one. When I did report people making fun of my stuttering even mimicking it at work to HR it only really ever hurt me. Then HR’s made it their goal to get rid of me. I only reported stuff when it got serious as well, such as to the point of mimicking me. Reporting it at school shouldn’t lead to blow back or vengeful behavior. But if this was a workplace, I wouldn’t report it since HR isn’t your friend.