As a fairly frequent SLF I know there are a number of airlines whose safety announcements include a suggestion to "keep your seatbelt loosely fastened whenever you're in your seat" and this always sounds like good advice to me. It surprises me how few people do this even if they'd never dream of doing a car trip without a seatbelt.
As for not even buckling up when the seatbelt light is on, I just hope none of these selfish prats land on top of me after they bounce off the roof.
Bob