It would be better not to overpass 10 players in order to make this game run smoother.
Arrange all players to sit in a circle.
It is quite simple to play. Everyone sits in a circle, and going clockwise we start to count as fast as possible. When someone reaches number 7, or a number that contains 7 [i.e. 17, 27] or is divided by seven [i.e. 14, 21, 35] must say Boom instead. If you do not then you take a drink. After several rounds,it becomes very hard to overpass 21.
in order to make it even more challenging every time someone says boom,we automatically start to count counter-clockwise.