One of the things that irritates me most in the world. And what irritates me more is that airlines don't seem to care! Some prick flagrantly abuses the cabin baggage allowance with a case that would never fit in the "Test your bag here" things in the airport, walks on to the plane with it, takes up way too much space in the overhead bin, and then by the time the second half of the passengers are getting on, there's no room left and they force people to put their bags in the hold. Outrageous!