The object of Boong-Ga Boong-Ga is to score points by spanking or performing kancho on a model of a human posterior embedded in the game's cabinet. A plastic finger is attached to the machine for players to perform the latter.
The game features eight characters players can punish: "Ex-Girlfriend", "Ex-boyfriend", "gangster", "Mother In Law", "Gold-digger", "Child Prostitute", "child molester" and "Con-artist". During gameplay, the facial expression of the chosen character is displayed on a monitor.
The game also dispenses cards that rate players on their "sexual behavior", and for players who perform exceptionally well the machine will dispense a small plastic trophy in the shape of a pile of feces.
Source: Wikipedia, "Boong-Ga Boong-Ga", available under the CC-BY-SA License.