The aim of the game is to count to 21. You can say up to 3 numbers in your turn. If you say one, the next player must start from the next number, if you say 2 numbers, the direction is changed at it is the previous player who must continue counting, if you say 3 numbers, direction is maintained, but a player s skipped.
A direction is determined by the first player who must declare 'To my left' or 'To my right'. The penalty for not responding, for answering when it is not your turn, or any other indiscretion is of course to chug, when the error is made, the beverage is consumed and play starts again.
Sample game: players sit in order (more players = better):
The game is reasonably simple at this level, but don't explain the rules to newcomers, let them try to figure it out (that's how I learned). As soon as people get the hang of it though, change the rules. Replace numbers with Roman numerals (i.e.: I, II, III, IV…) At this point the game gets confusing: what comes after IIIIIIV ? And who has to say it?
Then when that is mastered (if you aren't all under the table by now) replace the numerals with words. For example:
It then becomes great fun…. Especially if there is a Zoe in the room. Other common variants use swear words…