To paraphrase The Matrix: Unfortunately, nobody can be told what Mao is; you have to see it for yourself.

I have never actually played a game of Mao, but for those of you who have the attention span of an Eloi*, I'll attempt to derive some basic Mao rules from ApoxyButt's write-up above. (Correct me if I'm wrong.)

It starts with Crazy Eights or Uno...

...and makes these basic changes:
  • The wild card is not necessarily eights, and the suit of a wild card is called by the first to call it. There is a Point of Order in case of a dispute, but this is somewhat complex and requires additional analysis (later).
  • Say the name of the card you play (e.g. "9 of spades").
  • Say the one card left phrase when you play your second to last card. For example, in a game set up to be like Uno, the one card left phrase would be "Uno!"
  • Say Mao when you play your last card.
  • Do not talk out of turn.
  • As in most sports, there is a delay of game penalty. If you fail to play a card within about five seconds, or you have no legal plays, you draw a penalty card.
  • If another player catches you breaking any of the rules within five seconds after you break the rule, the other player states the name of the rule, and you draw a penalty card.
  • Rules are enforced more strictly against newbies than against the dealer's friends.
  • Different versions of the game are played in different regions, starting with different basic sets of house rules, unlike the similar game Bartok whose basic rules are formalized and must be clarified truthfully on request.
  • At the start of every game within a match, the dealer adds (but does not reveal) one or more new rules. For those not experienced in Mao, figuring out the new rules and keeping track of all the rules can be extremely difficult.

The first rule of Mao

is you DO NOT talk about Mao. From the description above, I gathered that some of the more "interesting" rules in effect were:
  • When playing a seven, instead of saying the card's name, say "Have a nice day."
  • The one card left phrase is "Last Card!" spoken in a "First Post!" tone.
  • There may have been other rules in effect that are not mentioned in my write-up.
Thanks to WyldWynd and m_turner for various clarifications.

DISCLAIMER:

WyldWynd says "fortunately your WU is wrong enough to merely add to the confusion ;o)"

*The Eloi are the cute people from H. G. Wells's The Time Machine who look like those blasted Precious Moments figurines.