Bullshit! or The Fourth Grace.
Like the card game of the same name (AKA "I doubt it."), which plays on the joy of lying and the fear of discovery. Mark Twain described lying as "a recreation, a solace, a refuge in time of need, the fourth Grace, the tenth Muse, man's best and surest friend." It is also a fundamental language skill that should not be neglected.
- Give every player 5-15 blank index cards.