bender card
An imaginary card that you never knew you had until you are informed that you have dropped it. An instinctive glance at the ground is then instant proof that you are a member of this exclusive club.
written by Ke*in *ow*ey, approved by Log

Similarly, any response to a cry of "Oi, you've dropped your lipstick" would be enough to prove your gayness. But not for girls, obviously.
written by Ni*k *unt, approved by Phil

The more intelligent kids would mime picking up the card, looking at it and then saying "There's been a terrible mistake, this card has your name on it. And a little photo of you bumming your dad."
written by Lu*e T*nsey, approved by Susan

Another way of showing that you thought someone was telling fibs was to yell ITCHY BEARD and frantically rub your chin as though it was unbearably itchy. Also made more amusing by the fact that when headlice were doing the rounds one year we had a teacher with a beard who got them and couldn't stop scratching his chin, cue hurt look and wails of 'but it's true sir!' much to his bewilderment!!
written by be*ki m*ss, left hanging by Edward