Official Rules to Bullsh*t/Cheat
The game is generally called Cheat in the U.K. and Bullshit in the USA. The aim is to get rid of all your cards by playing them to a discard pile. The cards are played face down, giving players the option to lie about the cards they are playing, but if the lie is exposed they must pick up the entire pile.
In this game each player plays the next rank above the previous player. Please note that there is another game, also known as "I Doubt It" or "Bluff", in which all players are required to play the same rank until there is a challenge.
Players and Cards
The game can be played by from 2 to 10 players. One standard pack of 52 cards is used.
All the cards are dealt out to the players; some may have more than others, but not by much. The object is to get rid of all your cards. Select at random who should go first and continue clockwise.
On the table is a discard pile, which starts empty. A turn consists of discarding one or more cards face down on the pile, and calling out their rank. The first player must discard Aces, the second player discards Twos, the next player Threes, and so on. After Tens come Jacks, then Queens, then Kings, then back to Aces, etc.
Since the cards are discarded face down, you do not in fact have to play the rank you are calling. For example if it is your turn to discard Sevens, you may actually discard any card or mixture of cards; in particular, if you don't have any Sevens you will be forced to play some other card or cards.
Any player who suspects that the card(s) discarded by a player do not match the rank called can challenge the play by calling "Cheat!", "Bullshit!" or "I doubt it!" (depending on what you call the game). Then the cards played by the challenged player are exposed and one of two things happens:
if they are all of the rank that was called, the challenge is false, and the challenger must pick up the whole discard pile;
if any of the played cards is different from the called rank, the challenge is correct, and the person who played the cards must pick up the whole discard pile.
After the challenge is resolved, play continues in normal rotation: the player to the left of the one who was challenged plays and calls the next rank in sequence. The first player to get rid of all their cards and survive any challenge resulting from their final play wins the game. If you play your last remaining card(s), but someone challenges you and the cards you played are not what you called, you pick up the pile and play continues.
If there are a lot of players, you may use two or more packs shuffled together. For some people the sequence of ranks which have to be played goes downward rather than upward, beginning A, K, Q, J, 10, ...
Some people play that you can (claim to) play either the next rank above or the next rank below the rank announced by the previous player. For instance if the player before you played some cards an said "two tens", and you do not wish to challenge, you have a choice of playing jacks or nines.
Some allow cards of the same rank as the last card to be played, as well as the next higher or lower rank.
In the Chinese game known as 吹牛 (chuī niú = bragging) or 说谎 (shuō huăng = lying) played in Fujian province, there is no restriction on the rank of cards to be played except that the cards in each set played must all be (claimed to be) equal. It would therefore be possible to play the whole game without lying, but then it would take you more turns to get rid of your cards than a player who was able to lie successfully. This version is normally played with several decks shuffled together, so that a player can claim to play a large number of cards of the same rank without it being an obvious lie. This game is described in Mae Channing's blog.
Some play that you can try cheat by playing more cards than you claim to have played - for example say three eights while playing three eights and a jack. This can be challenged in the usual way and you pick up the discard pile if your play did not match your call.