Reader's assumptions, I suppose, are a huge deal for me. When someone picks up something I've written and, when they're done, says something like, "I thought you were writing about zombies? This wasn't gory or scary." It always seems like they're looking down on me for taking something in a different direction than the norm... that irks me quite a bit.
When people compare my writing style to famous authors... mostly, I think, because I'm always compared to authors I've never read before, so people saying things like, "I can see the (insert author's name here) influence in this!" really gets my goat. Not to mention the fact that, while I have a distinct 'flavor' that I've developed on my own, I try to write in various styles all the time. Example: I'm working on a collaboration, and we're going for a very Douglas Adams feel to the style, but on another side I'm working on a different collaboration that's a straight up, hardcore nod to Poppy Z. Brite. So...
Poetry. Aside from haiku, I have no interest or desire to even look at poetry, and I've heard multiple times that NOT writing poetry makes me seem unromantic... and considering the fact that the underlying thread of most of my writing is attempts, in one form or another, at unconventional and unexpected romantic notions, that always bothers me.