I love Mike Spille's blog. He doesn't post terribly often, but when he does it's always worth reading. Here he is with a savagely funny mock of XP.
Rule 0. Whenever you type an 'i' - drink!. Also known as the zeroeth iXP rule. While the vision began with Alternate Letter Pair Programming Order, mentioned below, it's really this rule that made iXP gel, and which differentiated it from previous similar practices.