Oz- I don't hate him but he never really did much, yet he's loved by the fandom, why? Sure, there's no reasons to hate him, but there's no reason to love him either. Plus he's academically lazy which is annoying. He's not an idiot but he can't be bothered to put the effort in which seems like an insult to Xander who, despite trying his best, still didn't do very well on his exams.
Clara from Doctor Who- I hate her more than Kennedy which says a lot. She killed Doctor Who for me.
Phoebe from Friends- I found her ditzyness annoying in the later seasons.
Robin from HIMYM- This could be because the show was more geared to be from Ted's POV but it seemed to go out of its way to present Robin as the sun shining from her backside.
Rory Gilmore- Again, the show seemed to try and present her as the sun shining out of her backside. I began disliking Rory during the later seasons. I've not seen the revival because apparently she's even worse in that.
Mikey from Recess- He's so irritating.
The Rugrats from Rugrats- It became annoying how often they got the wrong end of the stick.