Merril, Anders, Carver, Isabella, and Fenris annoyed me a lot in Dragon Age 2. Merril with her whole "Blood magic isn't bad because I can use it correctly. To prove that I will go against the wishes of my clan!" thing going on. It actually wouldn't have been so bad if she actually followed through with it. But no, she had to try and do the whole mirror thing, and she has absolutely NO problems with demons. Really Merril? Plus her cuteness just didn't win me over. Felt she was a carbon copy of Tali, but felt Tali was better done.
Anders...can't talk too much due to spoilers. But seriously, he should have learned to not be so damn depressing! That and the whole "Every templar is against us!" and "Did you just talk bad about Mages? You are a horrible person who deserves to die!"
Carver was pretty much like Anders, except with a distaste for Mages. Well, mages who are hunted by the Templars (regardless if they are guilty or not) anyway. That and the whole Rivalry thing he has going on. I'm trying to NOT be a jerk to you, yet you still treat me like crap! Why? You want to make a name for yourself? Go ahead! I'm not trying to overshadow you like you claim to be! Damn! But whatever, I can tell he is a good hearted person.
Isabella, I think maybe you should probably cut back a bit on the whole "I'm a sleazy whore" image you have set up for yourself. You want to be one? Fine. But not to the extreme that you take it! Also, that whole Act 2 thing? Yeah, won't say due to spoilers, but seriously Isabella? Seriously? Then she never came back to my party because I didn't have enough Friendship/Rivalry points...
Fenris is the like Anders 100%. Hates Mages with a passion. My male Hawke was a mage, so I thought it would be interesting to romance Fenris. Sadly, Fenris doesn't exactly change his opinion...at all. I totally see where he is coming from, but like Isabella, maybe you should learn to calm down a bit?
Funny, I like how in DA2 they all have nice long character arcs/missions that you can go on, but I just felt like I couldn't really influence how the characters thought at all.
But the one, single, most hatred I have for a character, has got to be Kratos from God of War. Specifically, God of War 2 and 3. Extra Credits pretty much nailed my opinion of him perfectly. Sure, I felt like a Badass when I played as him, but I hate him so much. Its ok to destroy the world as long as you "Have your revenge!!!!" right? Actually felt really bad for the gods for being all "You said my name, now you must die!".
Yeah, slight exaggerations for the characters above, but they just annoy me so damn much...