River Song from the new Doctor Who series? I've only actually seen her in the Library episode, where she interacts with the Tenth doctor, but she was kind of insufferable, what with having his screwdriver (he gave it to her! and her version is BETTER), and knowing his true name (which I'm pretty sure no other character so far save the Doctor knows, though maybe the Master does), and knowing pretty much everything about him. No, literally, having a diary of his entire personal history. All I could think was "Man, if this were fan-written and not canon, people would be calling for her head, seriously." And to hear that when she interacts with Eleven, she keeps being annoying, even to the point that she can fly the TARDIS better than the doctor, etc. I'm all for strong female characters and all (seriously! LOVE when the Companions kick ass), but he's the mother-loving Doctor for crying out loud!
Please, feel free to weigh in on this. I'd really rather go without intensely disliking Doctor Who characters, and she's the first one I've ever felt real, true burning dislike for.