Start out with four quarters set up in a diamond pattern.
The mark's goal is to get the quarters in the correct pattern...WHILE FOLLOWING THESE RULES:
#1: Only slide one quarter at a time, using only one finger.
#2: no picking up, pushing, or stacking of coins (only operate within the two dimensions of the table... and no using one coin to push another)
#3: hardest of all: each time you let go of the coin you're moving, that coin must be touching at least two other coins.
Secret: The REAL secret to this trick? The real secret is to wait. Set everything up, tell everyone the rules, and... wait. Wait as long as it takes. If you've already done the match trick,, then you've captured everyone's attention... this is where you translate that momentum into a free drink. This trick IS SO unbustable, that you can let people work on it all night, until finally, in a fit of desperation, one of them will BEG you for the solution. Tell them that you'll be HAPPY to share the answer with them... but you're just... so... darn... thirsty!
Before you know it, you'll have a free drink in front of you, and you'll have established a precedent of "pay for play"... you'll be happy to do your tricks, as long as the free drinks keep coming.