Itou from School Days. But he was designed to be hated. I'm going to have to try harder... let's see...
Actually, I'm finding it hard to distinguish between those characters I greatly dislike/have no respect for/have hatred for that's fueled only by their massive and undeserved fanbase. When looking at it like that, Sasuke comes to mind from Naruto.
But, as for characters that I hate simply because I cannot find a reason to tolerate them and aren't designed to be readily hated... I'm gonna have to look deep into the depths of my anime experiences.
In Ragnarok Online, I was once known as Athero, a noble Lord Knight whose only wish was that he swung his sword for a just cause.
TrueSilverFox and Mon_Ami roamed Caballa together in Trickster Online, searching its ruins of splendor.
Valeria, sworn only to her sword and herself, traverses Erinn in Mabinogi with her pet silver fox, Truesilver.
"Whoa, TrueSilverFox, girl! Anyone ever tell you you look like some sun-bronzed Greek Goddess these days?"