Jinx is a children's game with varying rules and penalties that occur when two people unintentionally speak the same word or phrase simultaneously.
Rules
A jinx can be initiated when at least two people say any same word or phrase at the same time. One of them then calls "jinx" on the other.
The game ends when someone speaks the jinxee's name, or the jinxee speaks. In the latter case, the jinxee loses the game, and often a penalty is exacted, typically a punch on the arm.
References
Jinx (children's game) Wikipedia(Text) CC BY-SA