Challenge Coin

A coin earned in military service. (Command Coin, Deployment Coin, or Rank Position Coin.) Used to challenge other military members or veterans in a bar. If you presented with a coin and don't have one on you then you are expected to buy them a drink. If you have a coin to respond back to them with then they are expected to buy you a drink. Hence completing the challenge.

Everybody had a challenge coin but me at the bar tonight.