I rarely hate characters. Very few EVER get on my nerves. I.E., Jar Jar never really bothered me. No, I don't like him, and I do think he's a poor character, but he just never brought out the hate in me.
That said, one character that I wil NEVER like is Ariel from The Little Mermaid. To date, this is the only Disney theatrical feature that actively pisses me off. Why?
She's a selfish, thoughtless Mary Sue who suffers no consequences for her actions, learns nothing from her mistakes, and goes through no development throughout the movie. Her motivation is just to get the love of a man whom she claims she loves after just watching him dance and play a flute and then save some of his men from a storm. When she doesn't get her way, she seeks the help of a witch who tried TO OVERTHROW HER FATHER (this was revealed not in the movie, but in the original cut of the villain song), and gives up her voice to the obvious cheat. When she fails to have the guy kiss her after three days, her father just goes ahead and takes the punishment for her while her love interest kills the villain. She solves NOTHING in the plot, and gets everything she ever wanted at the end without earning an ounce of it.
The character's popularity as well as the movie's confounds me. Yes, the animation and songs are great, and the villain kicks ass, but its just not enough to make up for an awful heroine and water-bland hero. Worse still is that I have to reluctantly thank the movie for revitalizing the 2D animation industry for at least another decade, as without it, the "Disney Renaissance" wouldn't have happened, which means Aladdin and Hunchback of Notre Dame, two of my favorite animated films, wouldn't have been made, as well as inspiring Warner Brothers to kick off their TV animation boom in the early 90's, which means Tiny Toons, Animaniacs, Freakazoid, and probably even Batman: Animated series(as well as the rest of the DC Animated Universe) would've never happened.
On a more minor note, I can't stand watching Starscream in the old G1 Transformers show. For having started a character trend of being a second-in-command who the boss knows he wants to take over and tries to at each chance he gets, he is embarrassingly bad at it. Watching him announce his plans WHILE he's doing them makes me facepalm every time. Even when Megatron lays the smackdown on him, both verbally and physically, I can't stand that he just doesn't destroy him because, watching the show, Starscream is actually pretty incompetent. That makes me like him less because second-in-command characters are often my favorites because they HAVE to be competent. Also, his voice is the closest to ear-sodomy-rape I think I've ever heard in a voice. But since I never really liked G1, this matters pretty little to me.