I read a wide variety of genres, including the back of a Cornflakes packet if I can't get my hands on anything else, and I expect certain things from certain genres, but there are some things that really irritate me.
Romance: why, oh why, is the lead female so often young and a virgin? And the lead male is strong and dominant? That's ok for YA, but us grown-ups often like a little more meat to get our teeth into. I personally like a heroine with a little bit of experience and a lot of attitude, and one who can give the hero a run for his money.
Fantasy & Sci-fi: so many made-up names, often with apostrophes in the middle of them. C'onf'using or what? I have enough trouble remembering regular names, let alone odd made-up ones.
Thriller: the hero/heroine being confronted by the villain who has decided to kill him/her, but in a convoluted way, giving the hero/heroine opportunity to escape (think James Bond). If I was the villain I would just shoot 'em and be done with it.
All genres: the villain/protagonist explaining everything at the end in an extended soliloquy.
I'm sure there are lots of other things that annoy me, but that's just off the top of my head!