Probably Minerva Paradizo. I was so disappointed with her. Colfer's made great female characters before: Juliet, Holly, Meg Finn. How did he screw up on this one?!
Ginny, (HP) I don't hate as much, but I dislike her. She confused me with a complete character change. This is probably really dumb, but because she was such a quiet character in the first 3 books and didn't seem hang around her brothers that much, it was a bit odd to see her as this tomboy with attitude problems. And the random bat bogey hex master thing and being the 7th daughter of a 7th son or something. I didn't think she was well developed at all.
Edward (from Twilight) is annoying and he's too stupidly handsome and perfect and annoying. The whole idea of sparkly vampires is made of fail from the start. He also shows traits of an abusive boyfriend, as described in the link below.
http://www.gaiaonline.com/forum/recycle ... .26745143/
I don't like Claire from heroes, because she has the same trust problems with her dad over and over again. I find her to be a pretty boring character.
I found Misa from Deathnote really annoying as she simply doesn't fit the series, which is centred between the battle between Light and L. It was mainly her voice and airhead character that annoyed me the most.