sexual harrasment

Today at school I was sexually harrased so today I was in the book room and this guy had his hand around my neck calling me his girlfriend and etc. (I'm totally fine With that) so he then turned me around to where my butt was facing my "friend" he pointed at my butt and said "I'll hit that" "her ass is fat" he then tried to pull my pants down and touch my boobs...  I though it was normal from the weeks ahead of the this incident because my dad tought me if a guy says nasty things about you its love and I've never felt more uncomfortable in my life. What should I do?