Quite possibly the most pointless, yet funniest and most randomest thing to ever do. See also Hair.
Up and down.
See also Old-Timey.
Often used during a test. Or in a airplane.
Dude. Do us a solid. Add your own funny thing to do.
If you're the person across the table, you don't really know when to stop saying "Bless you." After awhile, you wish they'd sort of just knock it off.
See, for example, the James Bond film Thunderball.