How should you react in a situation where a guy insults you in front of everyone and continues to do so?

I insulted him back at first but then just tried to stop giving a shit and continued his joke about myself (trying to show I didnt give a fuck). However, I really wanted to just fucking hit the guy.

How would RP address a situation like this? How can I get above his level? What should you say to someone who insults you for no reason?