When three or more persons partake in the act of stroking their own sticks or flogging their own dolphins in a group until their jimmy's jiz.
When Tom and Dick were masturbating they felt lonely so they invited Harry and they all gang-bated. Prettysoon every Tom, Dick and Harry were gang-bating.
When sex with a watermelon that confuses gamers that listen to popularrapist gang City Morgue, the bigger the watermelon the more gang affiliated they are.
When two groups oppose each other for no apparent reason. Usually someone's sexuality has been challenged within a community and lines are drawn between those who agree and those who disagree with the accusation.