In most airports there are signs prominently posted informing people going through boarding check that all jokes will be taken seriously. So if you want to be some kind of smart-ass, you're sure as hell going to miss your flight (maybe even a lot of flights) while the authorities give you a very bad time.

Although this man was apparently not joking, as far as the sky marshals were concerned, whatever he said--or for that matter, however he acted--had to be taken seriously.

Don Firth