Akane from Ranma1/2. I just...I fucking hate this *****. She's just kind of...there. She never improves in her fighting abilities outside of one chapter only power-ups. Her entire character can be summed up as "extremely violent and insecure, and we have to be told she's a nice person constantly by other characters." Actively hitting people who annoy her with the power to crush stone. And she only seems to exist to be kidnapped, and side with the villains over the main character. And she's the main character's love interest.
Kagome from Inuyasha. I...don't like Inuyasha anymore. I like the character Inuyasha just fine, surprisingly, it's just how the story revolves around Kagome that kills it for me. She's a Mary Sue.
The Cerpenter family in The Dresden Files. Outside of Michael. He's cool. I just...don't like any of them, I guess. The mother just seems to hate everything outside of when something can help her, two of her children are just...there. And Molly...becomes kind of a ***** after a certain event on a boat that I won't spoil.
This one isn't exactly "hate" as more I don't really have much an opinion on. Luna from My Little Pony: Friendship is Magic. I much preferred Nightmare Moon as a character, in the two episodes we saw her in. I have nothing against the character, it's just that...we don't really know anything about her. Fans of her usually aren't fans of her, more than they are fans of their fanon version of her.
I didn't really like Pearl in Phoenix Wright all too much. It's less hate though. More...general dislike.