Yogi's Whist is closely based on normal whist, and is played with a full deck, with a single joker. Four cards are dealt to each player, and the top card of the remaining deck is turned up, the suit of which indicates the trump suit. Having looked at their cards, each player will choose one of the cards he has been dealt to place on the table in front of himself. This card is the player's bid, and its suit indicates the number of tricks that the player hopes to win. A diamond equates to zero, a spade to one, a heart to two, and a club to three (think of it as the number of blobs on the suit indicator). This order is also relevant in a number of other card games, and will often be called "Yogi's Whist order".
When all the players have placed a bid card on the table, each player, in the order to which they were dealt, has the opportunity to "declare", "reveal", or indicate that they wish to do neither by saying "no". If a previous player has indicated an intention to declare, the remaining players may either say "no" (and thus let the declaring player do so), or reveal. If a player indicates that he will reveal, no further players are queried.
We will come back to declaring and revealing shortly, and for now assume that all the players have said "no", in which case the players play in the order to which they were dealt. The first player will lead a card, and (as with normal whist) each following player, in turn, must place another card of the same suit on it if the player has one. If not, a card must be thrown away (on top of the played cards). If, unable to play a card of the suit led, a player plays a card of the suit of the card turned up, he will have "trumped" the trick.
Once all the players have played a card, the winner of a trick is the player of the highest card of the trump suit which has been played, if any, or failing that the player of the highest card which has been played (aces high) of the suit of the lead card. A joker counts as the turn-up card, both in play and when bidding. The winning player collects the pile of played cards and places it in front of him (to allow the other players to keep track of the number of tricks each player has won). The winning player gets to lead the next trick.
Once all three tricks have been played, those players who have "made" their bid (i.e. won the number of tricks that their bid card predicted) will place their bid cards on their foreheads, showing the value of the card, to allow fines to be calculated. Normally a finesmaster will be keeping track. Those players who have not made their bid will drink one fine (Yogi's is normally played with pencil fines) for each player who has made their bid, plus one. i.e. if five people are playing and two make their bids, the remaining players must drink a fine of three (pencils) each. The deal then revolves one player to the left.
Now for the bit that makes the game interesting: declaring and revealing. If a player chooses to declare (and no other player stops him by revealing), then after the first card is led the declaring player turns over his bid card so that the other players can see it. If a player has declared and makes his bid, two of the fining unit are added to the fines of all the other players (e.g. if one of the players who made in the above example declared, the other player who made would drink two pencils and the others five). If a player has declared and fails to make his bid, that player has four fining units added to his fine. Hence a player is wise to declare only if confident he can make his bid.
Revealing is a similar, but more extreme, concept. The revealing player turns over his bid card at the time he reveals (before a leading card is played), and can then choose which player will lead (he may choose to lead himself). After the first card has been played to lead the first hand, the player who has revealed must expose his remaining cards so that the other players can see them. Hence the other players can see any weaknesses in his hand and play to exploit them, if they can. If a revealing player makes his bid, all the other players have four fining units added to their fines; if he fails then he adds eight fining units to his fine.
Note that it's only making one's bid that matters, not actually winning tricks. Therefore the 2,3,4 and 5 of diamonds is a very strong hand (at least unless diamonds are trumps), and worth revealing on. On the other hand, unless clubs are trumps, the 2,3,4 and 5 of clubs is a very bad hand.
The last detail is that if, and only if, the card turned up as the trump card is a nine, then the nines form a suit of their own (with increasing value in the same order as the bid cards). A club and three nines if a nine is a trump card is therefore a very strong suit. Note that nines used as bid cards count as their normal suit. A joker as the turn-up card also makes nines the current suit. It's traditional not to remind people about nines until after the event.
Yogi's Whist was presented to the Club at a weekly Formal Hall by Nick Inglis on the 19th of May 1986, as a derivative of the three-player (mostly) trick-taking game Ninety Nine - not to be confused with the Ninety Nine that's the origin of Glengariff 99. Nick also introduced the pencil as a fining unit at the same time, despite Stew's protestations that this would "not involve enough drinking" (an objection that was shortly retracted). A blind, deaf bear at Knaresborough Zoo was dying with much media fuss at the time and the game was named in his honour. On anniversaries of the invention of the game, scores are traditionally kept for the evening's play (in addition, obviously, to fine drinking).
A variant of Yogi's, known (due to its appellation by Stew) as "Bloody Fucking Thing", gives the dealer the choice of the number of cards to deal to each player (though it has to be the same number to each). Bids are made in clockwise order from the dealer, and the player bidding must say the number of cards bid, normally in terms of the gifts in the Twelve Days of Christmas. Once players have no (unbidden) cards left to play, they are excluded from subsequent turns.
A rare variation is SEPTIC Yogi's, in which SEPTIC members get to vote whether to rotate everyone's bid cards one place clockwise.
CUTwC has an online implementation of Yogi's Whist, including fines. It's not as fun as playing in person.