Passengers not in J putting their luggage in J's overhead bins
This has always annoyed me, even when I'm not sitting up front. It really annoys me when I am sitting up front and board a bit later and there's no room for my carry-on.
This morning though, for the first time I've seen, a flight attendant made a passenger remove his bag after he put it up front and then walked to the back of the plane.
This should happen every time.