I would save files so I could reload the best sequences, or possibly redo them better (or possibly fuck them up, so I can do anything without consequences), and I would make myself more attractive, rich and not being a social reject (which I sadly am in many social circles). But I'd still be a total douche to stupid people.
Plus, I'd give myself superpowers (teleportation, regenerate health, practically anything you can find in Heroes. But I wouldn't use them for the greater good, cause REAL superheroes (like Batman and Rorschach) aren't welcome in the real world, cause everyone (including the police) wants to kill you. So either I'll become a brightly colored villain (like the Riddler) without being a total psycho, and I'll go around making some fun crimes, and don't give a fuck what happens to the world... And I would use my powers to impress ladies, even though they know I'm crazy evil. But now I've got off track.
Oh, and most important, I'd get back on the ones who bully me, by either making them ugly, weird, or stupid (no change there then)