Two or more drinkers sit around a table. The first starts a round with any number between 1 and 99. The drinker next to him adds 1 and so on around the table. If the number is a multiple of 3 or contains the number 3, that drinker taps the table. Otherwise the drinker says the number out loud. Anyone who recognizes a mistake can say so and the one that made the mistake must drink. Anyone that wrongly accuses someone else of making a mistake must drink. The drinker that just drank starts the next round with any number between 1 and 99. Note that if the starter selects a number that requires a tap then he must tap. But it is up to the next drinker to interpret that number correctly, but any way he chooses.

Examples:

1, 2, tap, 4, 5, 6 - oops, that last drinker must drink.
10, 11, tap, tap, 14, tap, ...
tap, tap, 25, 26, tap, ...
tap, tap, tap, tap, tap, tap, 40, 41, tap, ...
tap, 100, 101, tap, tap, 104, ...

Very simple, but surprisingly fun.

Same as above except:

1. 7 is used instead of 3.
2. Instead of tapping, the drinker must say '7 up'.
3. When someone says '7 up', the direction changes. This gives the wrong person a chance to mess up and speak out of turn, leading to a drink. It gets confusing and almost silly when the number reaches 70.

Coming soon...