Two pet peeves I have, and I admittedly have several more, but most of them are underwhelming and have been repeated here already. I'm just making a list because complaining is fun. >.>

1) Dialogue. The first problem is minor, and has only happened a few times, mostly with one person who isn't on the Guild, that I know of. But when someone typos a word or name in dialogue... admittedly this can be annoying for the person whose character is named, but typos happen. Not checking with the writer first before having another character call the speaker out on mispronouncing something can kinda ruin the moment, slight though it may be. The second is anyone putting words in my character's mouth. Knowing the answer to a question they're asked, in general, is fine. But actively writing out what they said, especially if they don't know how my character would have spoken, just makes me fume. Briefly. 

2) Giving my character personality attributes they never asked me about before sticking them in the story. Even if the character was from a wanted ad, even if we shared our ideas about them, and even if the two characters are supposed to know each other really well. If you get them right, that's lucky, if you get them wrong... One of us isn't going to be happy. I don't mind characters assuming things about other characters, or having their own perspective on my character's actions and thoughts, but literally making it a statement of self-assured fact without checking in with me pisses me off.