Can you imagine boarding a plane and not looking the flight attendant in the eye while you say hello? Or dropping your bags at a flight attendant's feet for him or her to store your stuff in the overhead bin? Or being the person who stands in the galley -- the flight attendants' only free space -- and talks to the flight attendants when they would prefer to be taking a break from passengers?
I can't believe people do this stuff. Actually, I've seen the people who stand in the back and bug the flight attendants, but I can't imagine people who are so rude that they don't even say "Hello" on their way into the plane. But, according to this interview on FareCompare, flight attendants encounter more than their fair share of rudeness in their jobs. Bleh.
Airline Flight Attendant Q&A