What do I do about him?

I was in a band for a while with 5 other guys. I had dated one of them( lets cal him john). Well, I guess he told his friend(lets call him jckss) that I was easy, so jckss kept trying to get in my pat. I finally tol him that I didn’t like him at all, and he got mad and called me fat. Like we were 5 years old or something. So, after I got sick of him acting like a spoiled little brat around me, I quit the band. I was fine for a while, but im changing highschools in august, and ill be in the same class as him. What should I do about him?