Well, nearly all the characters in FFXIII (except the 2 aussies), but I especially loath Snow, not only for the idiotic name.
Lars in Tekken 6, put in just for their silly juggling mechanic and he was nearly the only person you came up against online (well him and Marshall Law but he's cool).
Anders/Justice (aka Spirit of Vengeance) - this one is personal. They took a good character and turned him not only into a whiny idiot but one who's goals were stupidly misguided. He was the reason for Dragon Age 2's story and not my main character. I didn't forge my alliances to take out the bad guy, he was the bad guy in Dragon Age 2 and I knifed him in the back....every single playthrough.