One thing that tends to bother me is when people attempt to prove that something (consoles, games, movies, etc.) is objectively good or bad. If you ask me, they're just... things, and the perception of "good" or "bad" is entirely up to the person using it. Everyone has different standards. One man's trash is another man's treasure, you know?
Elitism also often bothers me, though that often goes hand-in-hand with the above point.
One more thing (this is more minor) is when I say something and then whoever I'm talking to feels the need to point out that what I said is just my opinion. Isn't that obvious? Assuming I don't say something is fact, it should be implied that what I'm saying is opinion. (Again, this is all kind of connected to the first one...)
I agree with pretty much all of these, especially the last one. I hate when people point out obvious things like its something so important o_o