Ditto on the seat-kickers with the indifferent mothers. If I had dared to kick someone's seat when I was small, my mother would have wasted no time in kicking me!!!

I also hate the people in Y (yes, I slum it a lot) who think everything in the row is theirs. E.g., people who take all the pillows/ blankets, people who insist that you open/ close your air nozzle thingie, people in the aisle seat who insist that the window shade stays up/ down, etc.

I also really hate the people who board late and then make it your problem when their carryon crap won't fit in the overhead bins. At least a half-dozen times I've been asked by people who boarded late if I would mind checking my carryon so that theirs will fit. And then there was this one time when some girl was taking everything out that could conceivably fit under a seat and handing it to random people telling them to keep it under their seat (even though it wasn't theirs). Granted, I am all about storing stuff under your seat, but in this case, it was mostly stuff from people sitting in the bulkhead (i.e., no seat storage).