J'te Gage Que... (2006)

"J'te Gage Que..." (in french) or "I Betcha" (in english) can be played during almost any other social activity, including another game.

Each player receives a card that features three challenges.
Challenge examples include "Speak three sentences in a foreign language" or "Suck your thumb for 30 seconds".
Everyone agrees on when the game will end (i.e. "In two hours.").
Then each player must perform/act out his three challenges in a subtle manner, but with witnesses.
If no one says anything for 30 seconds after a challenge has been performed, the performer can whip out his card and show everyone the challenge he's just performed. This nets him a number of points (as specified on the card).
If, however, another player says "I bet you had to suck your thumb [for instance]" and he's right, that other player earns 2 points. If he's wrong, he loses 1 point.

Whoever has the most points at the end of the game wins.