Northern Secondary School rules for Asshole:
You need at least three people, four is ideal, any more than five or six and the game becomes unwieldy, especially as you'll probably need two decks.
Take the complete deck of cards (including both jokers, but not including the rules for draw and stud poker card) and deal them out. I am using the numerical for the number on the cards, and the words for quantities. Four 6s means four cards with 6 written on them ;)
The first game
Whoever goes first (decide yourselves, or let whoever has the 3 Diamonds) must place a card or cards on the same table. If multiple cards are placed, they must be the same number. Each subsequent player must then place an equal number of cards for their turn, or pass. Cards are ranked firstly by number, and then by suit.
RANKS OF CARDS:
3 (lowest) -> Ace (highest)
Diamond (lowest) -> Club -> Heart -> Spade (highest)
As an example, the 4s of Spades and Diamonds could be placed on the 4s of Clubs and Hearts, but not vice-versa. If someone had place the 4 Spades and Diamonds already, you could not place the 4s Clubs and Hearts (since Spades outranks hearts) and would instead have to place two 5s of any suit or higher.
The 2s and Jokers are special cards. Placing a 2 instantly wins the hand and lets you start the next hand, unless someone places a 2 of a higher suit atop yours. A Joker is the ultimate card, beating everything except another Joker, or multiple Jokers.
USE OF TWOS AND JOKERS:
One or two cards placed - one 2 or one Joker
Three cards placed - two 2s or one Joker
Four cards placed - three 2s or two Jokers.
(note anything beyond this will start arguments as to how many twos you need for six cards, and is why you should avoid playing with more than six people or multiple decks)
The hand continues with people placing successively higher cards on the pile until someone either decisively wins with a 2 or Joker, or everyone passes. Push the pile aside, and the last person to play (if there is no Asshole) starts the next hand.
Winning the Game
The first person to completely get rid of their cards is the President. The next is the Vice President. The third is the Vice Asshole, and the loser is the Asshole. For five player games, the third player is 'neutral', and for three player games the second player is neutral, between the President and Asshole.
Starting the next game and subsequent games
The cards are shuffled and dealt. The Asshole *must* then give their two best cards (highest suit and number if no jokers or 2s) to the President unless the President specifies otherwise. The President can then give whatever two cards of their own that they like to the Asshole, although sportsman Presidents may ask if the Asshole needs anything in particular. Similarly, the Vice President and Vice Asshole do a swap, but only for one card. Neutral players are stuck with what they're dealt.
The first hand is then started by the Asshole, and then turns proceed around the table as normal.
Whoever has threes, especially the 3 of diamonds, must endeavour to win a hand so they can then start the next hand by placing them, as there is no other way to get rid of them. For the Asshole, the more 3s they can get the better, to increase the odds of their winning the first hand with all four 3s and getting to start the next hand.
It is wise to keep a two or joker in reserve until near the end. Particularly stylish players will win a hand with a two, then then next with another two, then the final with a Joker, shouting 'OHHHHH!' very loudly. If someone tries to beat your two with their own and then you slam down your Joker, you may wish to stand and do a pelvic thrust and say, "Right up there", or they may wish to grab the table in a about-to-flip-it-over-like-in-Westerns-when-someone-is-cheating way. At least, that's what we did.
It may seem entirely possibly to dominate while President, but a skillful Asshole can easily dominate an entire game and take the top spot.
Especially while learning the game, arrange your cards in your hand in numerical order, to speed up the game.
Although you are allowed to pass, this could mean you miss a chance to get rid of lower cards, in case you've got two 8s and pass on putting them atop two 4s, and the girl after you lays down two Kings.
Each social group at NSS had their own slightly different rules, such as Chinese Asshole (which was not intended in any way to be racist, we were a racially diverse school and it was an inside joke between two buddies, one of whom was Chinese) where I believe threes were wild, or another variant which removed the superweapon factor of the Jokers. RPGeek has submitted a variant where you switch seats so each round is played in order of rank.
Asshole was the official sport of NSS for most of my five years there (yes, five years, OAC year) and people could be found everywhere in clustered groups, asking, "who's president?" before grudgingly flinging jokers at the person next to them.
UPDATE 16/05/2008: If you're interested in trying Asshole, it is available in 42 All Time Classics/Clubhouse Games for the Nintendo DS (albeit called 'President'). Unfortunately, some of the rules are downright loopy (there's a 'revolution' which means all cards get reverse values of someone plays four-of-a-kind, you need as many twos as the number of cards you're trying to trump, and jokers aren't as powerful. And my years of practice allow me to crush even the hardest AI with ease. Still, I can get my 'fix' for the first time in years.