If you don't know, a "challenge" is a kind of a drinking game. The challenger presents his coin, usually by placing it on the bar or table in a drinking environment, sometimes by tapping the table or bar with it repeatedly. Traditions vary.
Those who regard themselves as members of the group are obliged to present their coins or buy the next round of drinks for those who do. If all declared members present proper coinage, the challenger buys the drinks.
There's additional protocol. The coin may not have been made into any type of jewelry like a belt buckle or key chain. It's okay to do that, it's just no longer a valid challenge coin. However, a coin worn as a necklace is still a valid challenge coin.
I wish I belonged to a group which took the rule of law seriously enough to use a challenge coin like this one pictured, which was a fundraiser for the political action committee named at the bottom of the coin. I'm carrying it anyway.
