The last remark spoken in a social situation that causes an awkward silence due to a breach of etiquette in a previously light-hearted situation of escalating banter.
Named after the game Jenga in which a tower of wooden blocks is created and each player carefully removes one wooden block, in turn, from the tower until one player removes the fatal block causing the collapse of the tower, and subsequently loses the game.
Person A: "Hey, I just got back from Disney World."
Person B: "What did you bring me?" (Joking, knowing the answer is nothing)
Person A: "I brought you back Mickey Mouse, but he died in my suitcase in the cargo hold so his body is a bit decomposed now." (Possibly pushing the limits of social etiquette in this situation)
Person B: "That's ok, hack off his ears and make a hat for me." (Pushing the limits even further)
Person A: "Are you sure you don't want a coin purse instead?" (Exceeding the limits of etiquette in this situation)
The last statement by Person A is the Jenga Joke.