Four Finger Pain Train

The four finger pain train is a controversial practice commonly used by boorish Neanderthal girlfriends in order to dominate their significant other. It involves the sudden unannounced insertions of the four non-thumb digits of the hand up to the hilt into the partners anus. This usually causes the the victim to writhe around in agony for several minutes. But in rare cases can be greatly enjoyed by the recipient.

When 4 people do something sexual with each other in one night. Similar to a three sum but with 4 people.