I dislike meaningless character death. If there's any other option, it's a huge pet peeve of mine to have a character killed off just to "up the stakes", or because the author for whatever reason doesn't think it seems "real" enough. That'll be the handiest way to turn me off a story, whether or not I liked the character at all.
Something else that always bothers me is when characters are written unsettlingly prudish, but it's not because it's organic to the character; I find it annoying when it's because of the author either following a trope (such as the all too common one popularized by various anime where the main female protagonist is upset to the point of physical assault by seeing a mostly-dressed guy changing his shirt or something similar; naturally, it's played as if it's his fault despite it almost always being hers) or using the character as a mouthpiece for author insecurities.
It's fine to me if there's an organically prudish character, because you can do something with that. That can go somewhere and be explored, especially with things like the character getting a little tipsy, or having an upbringing that shaped their worldview, for example. In fact, I'm working on a collaboration with a wonderful author who has a bit of a shy and reserved character, and of course mine is the opposite -- you can do so much with it, handled well. There's so much potential there.
The stuff I find irritating is more often stuff that comes out of nowhere, and it drives me up a wall. It's like the author regards it as expected, and in turn expects the audience to agree.
