One thing that drives me crazy is travelers who insist on not ever checking a bag but lug around giant odd shaped carryon bags that take up two spaces in the overhead bin.
I get people not wanting to check but this is ridiculous. I saw a guy and his wife who each had a big camping backpack with 20 pockets completely jam packed. The person at the gate was too kind to tell them they were too big and needed to be checked so they crammed them into the overhead and that made us so others didn’t have the room they needed.
People need to show some common courtesy. That is why you get to your seat early. So these type of people can’t hog the overhead bins. Rant over.