Ignoring content, A closed mind that's really only looking for one specific answer, like a question trying to rally up a pity party, or, like you said, someone who puts down answers he doesn't agree with. Why put down someone who went through the trouble of trying to answer your question? I flinch at bad grammar, but usually it doesn't matter unless it's coupled with a really ignorant person. And then there are the people who ask an alright question, but are subconsciously looking for an answer that makes them feel better, so they start commenting answers trying to "make their question more clear" because, obviously, the answerer wouldn't feel that way if they "read the question right."
If what is asked is something I don't know much about. Needless to say, dating, flirting, relationships or sexuality questions, since I'm not an expert! Unless, it was something I know! Basically, uninviting questions.
Bad grammar, subject line doesn't grab my attention, "choosing between two guys/girls", troll/offensive questions, pity parties, and religious/political questions (I avoid them as much as I can, but sometimes I do answer them). And like Marelade said, id I can't think of a quality answer or I don't understand the question.
Redundant questions, or boring topics. Also lists questions, I can't stand to ever do another again. The other being too much information. If you want help, make your message clear and to the point. Excessive rants only tell us you're not really looking for advice, but encouragement to continue whatever it is you are doing wrong.
I avoid questions that include too much excessive detail that is needless and takes away from the main thesis of the question. I have a short attention span and I can't handle so much needless information.
For me... it's the fact that I hate giving advice for something if I haven't personally experienced the situation at hand. I know I can sympathize but I can't empathize until I spend some time in their shoes so any advice I'd give would be bogus.