Fool's Bluff is a cards betting game that can be played by two or more players.
The basic game is simple - each player is dealt a card which he does not look at and holds up to his forehead such that every other player can see it but he cannot. The players then perform rounds of betting upon their cards and after all rounds are finished the player with the highest card wins the pot.
To avoid the embarrassment of asking, make sure to specify if Aces are high or low before the game starts!
While fun on its own the game is best played employing one or more of the following silly variations and with two to four players.
Allow players to pay a chip or more to the bank to "buy" an extra card to place on their head. This gives them a better chance of having the highest/best card and can also switch up the game in the middle of the betting rounds.
It seems important to play with some form of blind, otherwise players don't have much motivation to play. This becomes even more important with more players when it is almost immediately obvious if you don't have a good enough card to win.
Instead of betting chips or money why not try wagering fingers of drink on your card. The winner drinks nothing and any of the losers drink their full bet at the time they fold or lose.
Be warned - this drinking game will almost certainly get everyone very drunk and very silly, very quickly. After raising the bet to over 100 credits don't think a player wont try to buy the rest of the deck in an attempt to get himself out of 50 fingers of drink.
Fool's Texas Hold' em
A good version is to play Texas Hold' em and on the initial deal have one card in hand and the other card on your head. This gives you and other players only half an insight into your hand.
alternately Fool's Bluff can be paired with just about any other poker variation in similar ways.
How about after rounds of betting some player must announce the card of one of the other players, until after N number of rounds each player knows what their card is.
Alternately one could have a variation where each player must say the card of each of the other players without having to tell the truth and so each player must somehow work out what their own card is and is rewarded somehow for getting the closest prediction.
Really anything goes and there are lots of cool variations which can be thought up. One real theme seems to echo between the best rules is simple - the sillier the better.