I hate:
Rage (Reiji) from Gravitation: In my opinion, she single-handedly ruined the manga... It was her arrival that made the WHOLE thing get off-track. But I will admit, she IS kind of funny in Gravitaiton 2.
Ayaka from Gravitation: She's just annoying and pointless and Hiro is too good for her.
Hideki from Chobits: Oooh, don't get me started on Hideki... He is SUCH a pervert and is in NO way deserving of poor innocent Chii!!
Nagisa-sensei from Loveless: She dressed Gothic and Lolita, so I thought I'd like her, but she is annoying, a waste of screen time, and she hates the male Zero team and Yamato. I LOVE the male Zero team and Yamato.
Rubette from Gokudo-kun Manyuki!: She's EVIL I tell you, EVIIIIL!
And I hate TONS more characters that I may or may not rant about later...