It's rare that I'm annoyed by a character, actually. I can be frustrated by characters, and I can be horrified by their behaviour, but sheer annoyance is rare, thankfully.
There is one, though. A girl about whom I have read recently. She does not grow up or change in the course of a novel, she thinks it makes sense to head out on one of the most dangerous nights in living memory, she doesn't think about the consequences of her actions.
I'm talking about bloody Kiska (and that is how I referred to her in my head whenever she came 'on-screen'). I read her story in Night of Knives by Ian Cameron Esslemont. If Mr Esslemont intends Kiska to be an annoying character, then he succeeds beyond imagining. If he thought she would be beloved by readers, then, boy, he pitched her wrong. I found myself gritting my teeth at her attitude, her dialogue, her innate recklessness. Bah! Just thinking about her is making me feel all riled, so I'm going to quit while I'm ahead and look forward to Day 7 *grins*