Calmly talk to him/her about it and if he/she does not stop, tell an adult.
As a student, to stop or minimize bullying, you have to try and befriend the bully, try to know her/his problems because every bully has a dark past and you have to understand them in order to help them. This is really helpful, and its true that the bullies always have their dark past, either that or maybe they have something bugging them, hot-headed people use people to let out their anger to be able to relieve their anger.

Hopefully this can help minimize the bullying, this might not work 100%, but at least you can try to help and in the process, you can socialize and gain new friends.