I'm going to break a classmates nose because he called me a worthless slut
What caused him to call that?
He sexually harassed me at a party and I slapped him.
Words should not incite violence, don't assault him. Report what he did at the party and move on. He could be dangerous if he hit you back.
I'm not going to report it, I just want to get revenge for what he said.
While what he said is abhorrent you should report it and not use violence. If he decided to hit you back in self defense you could really be hurt, or killed if he is angry enough.