21

OK, modeled on the drinking game. Sit in a circle, count up to 21. The 21st gets to make up a rule, like saying Buzz on the primes, swap seats every fifth number, reverse counting, etc. Mistakes are penalised. First I penalised with points (the person with the least points wins), but then used a forfeit. Anybody who made a mistake had to either dance for ten seconds, sing for ten seconds, or talk English for ten. Fun times were had, and a compromising video of the teacher dancing was recorded, so I'm going to call that lesson a success.