Just a hand
Get everyone to join your club
The peron in the know will hold up a hand (doesn’t matter which hand and it doesn’t matter if the palm is towards them or not) and touches each finger in their hand starting at the pinky saying Jimmy Jimmy Jimmy Jimmy woooo Jimmy (reverse) woooo Jimmy Jimmy Jimmy Jimmy(the wooo is when you get to the area between the pointer finger and the thumb – you slide your finger down the pointer finger and up the thumb). Then cross your arms and challenge someone else to join the club.
The goal is to get the people to try and try this over and over again changing the hand they use, the position of the fingers, etc trying to join the club until they finally realize that they need to cross their arms at the end.
Once you are down to a few people not in the club start making the arm-crossing more and more obvious so they finally catch on.