I liked the tale of a Virgin Atlantic chief stewardess (or whatever the current PC term is), who announced that due to a short turn round time, they needed volunteers to assist in tidying up the cabin -and anyone wishing to volunteer could make themselves known to the cabin crew by standing up before the belt signs had been switched off!
It must be so tempting to say "Please pay careful attention to our safety brief as questions will be asked afterwards. Any passenger unable to provide a correct answer may be off-loaded....."