Villains/antagonists or otherwise.
I’ve been watching some Fable 3 lets plays and was reminded of how much I absolutely hated Reaver. You can tell Lionhead was really going for someone that you would “love to hate,” but every scene with him in it is miserable. Absolutely ridiculous that you can’t kill him.
For a character from an actually well written video game, Eric in Tony Hawk’s Underground. Hitting the last line in the game and watching your character punch him out in a cutscene afterwards is extremely cathartic.
Handsome Jack. Most people find him funny-hateable, but I just found him gratingly annoying. I got two hours into BL2 and quit, then never came back. Which was a pity, because I was playing it with my wife and we had a blast with BL1.