What ticks me off are those passengers who think the rules don't apply to them. They're either too dumb or don't have a clue - but generally act that whatever they do is fine - with a careless, cavalier attitude regarding the rest of the passengers on the plane.
I also have little tolerance for those who upgrade from economy to first/business - and think it's their right to be up front.
Kids in all classes who aren't managed by their parents are a pet peeve.