Sosuke Aizen (might count as a spoiler, but by now, I don't care), Sasuke Uchiha (if only to stop him from being a whiny *****), Bella Swann (and possibly Edward Cullen, if not for the whole "diamond-like skin" thing), Hannah Montana (though for this one it'd be more of a slap than a punch), and Professor Umbridge (for obvious reasons).
I'll add more if I can think of any.
EDIT: Got some more- Porter C. Powell and Henry Masterson (from Transformers Animated, for those of you who don't know), Eragon (again, for obvious reasons), and Kurata (from Digimon Savers/Data Squad- fans of the show should know why).
EDIT 2.0: Peter Griffin/Quagmire/Brian (for various reasons), Peter Parker (post One More Day for VERY obvious reasons), and Berii Shirayuki (from the so-called "sequel" to Tokyo Mew Mew).
Er... let's just say there's a lot of people I'd like to punch and leave it at that.