She’s the one I dislike the most – she’s gotten so very very mean.
Leonard’s mother on BBT – she is so utterly selfish, self-absorbed, cruel, and actually evil. I can’t watch any episode she is on. But I would like to know that, sometime, Sheldon’s mother meets her and thoroughly spanks her/puts her in her place/teaches her to become a human being. Or else slaps her out of the universe.
Does Chuck Lorre have mother issues?
I hated Boxxy the Robot Dog and his kid owner on the original Battlestar Galactica. The one who would INEVITABLY run out and bark at the Cylons whenever they were around. I so wanted both of them to be give a merciless curb-stomping by a Cylon patrol. But it wasn’t just them that brought the hate, though they were enough. It was that they encapsulated all the stupid that went into the show. They represented the fact that although Battlestar Galactica (the original) could have been great adult SF fare, they went with a kiddie show, because the nimrods in TV production were sure that’s what SF was about.
Hmm, the mom on 2.5 Men is pretty brutal as well. I liked both the moms on Dharma and Greg; in fact, Kitty (Susan Sullivan) was my favorite character, followed by Jane.
I used to hate Eli, but after last week I am changing my mind.
I think he’s admitted as such when discussing the mom on 2 and a half men.
Granted, she’s about the best thing about the show.
Cally on Battlestar Galactica.
I liked her initially, but she eventually annoyed the crap out of me to the point where I actively rooted her to be killed.
During the episode where she and Tyrol had to get flushed out into space I remember being furious when she survived and cursed Ron Moore for giving us a death tease.
Meathead on All in the Family. Even when I was a little kid and I knew was supposed to hate Archie for being a bigot, I was always aware for all his faults and flaws, he was a better human being than the Meathead who was perpetually arrogant, condescending, and intolerant of anyone who disagreed with him.
Also, I’m getting way fed up with Lip on Shameless. Every single scene he does he’s sticking a cigarette in his mouth.
Penelope García and spencer Reid on Criminal Minds
García constant constant introductory phrases, the “oohhh-awwwww” how cool is my techonolgy thingy, and her “I´m about to cry” shtick.
Reid´s Sheldon-meets-Grissom and completely useles trivia and phrases make me root for the criminals.
I’m only on the second season of Sons of Anarchy but I can’t stand Tara. She never changes expression. Occasionally she has moments of awesome but they’re few and very far between. For a doctor I think she’s pretty freakin stupid as a person. Does her character get more tolerable later on?
Veronica Hammel may have been annoying to watch, but she was a lot more pleasant to look at!
Jim Halpert on The Office. (If I worked with Jim in real life I would stab him in the face.)
Wimpy Spike on Buffy (I know this subverts the intent of the question a little)
Any child
Because nobody likes that show.
Be nice, Lauren Bacall couldn’t have made that character bearable.
Whoopie’s character on TNG was so godawful I always suspected it was a deliberate trolling of the fans.
Different strokes about her annoyingness–I always thought the chemistry between her and Furillo was one of the best parts of the show (that, and Belker) 
Fay was definitely annoying, though.
On Breaking Bad, I started to hate Jesse – he made just too many unbelievably stupid decisions, and it’s also not believable to me that someone so sloppy could ever come remotely close to rivaling Walt’s product without Walt’s constant supervision. It strains my credulity too far.