The only anime character I absolutely cannot stand is Sasuke Uchiha. Mainly because I'm tired of the whole show being centered around him, he's a jerk, he's stupid, and anyone who agrees to move in with Orochimaru has to be completely insane... and I do believe he has enough fangirls flooding the Earth.
ALSO, I find his arrogance extremely annoying, to the point where I would shoot him in the face if I could.
Other than that, I really don't mind Sasuke...
Oh, and the other characters I don't like would be Orochimaru, Kabuto, and Danzo.
On other anime, I don't see the point in Onigiri on Air Gear... I mean, I do, but I don't, it confuses me.