It bothers me, with my OCD tendencies. I'd like to sweep through the boards tidying them all away into their proper places 
But, more seriously, what really bothers me is that there is a type of poster who only posts in AIBU, and who doesn't know there's anywhere else on MN.
Then there are the other posters who do the same, but who also think that the whole argy bargy of it means that they can jump in and have a go at anyone - regardless of the original OP or question. I've seen some shocking things said to other posters there, and then posters justifying their unpleasantness by saying "well, this is AIBU, what do you expect?"