When two men share the same room and sleep on different beds, they eventually get to know each other and discover their homosexuality. After having gay sex, the taker is considered to have had his "Mattress Popped", and therefore sleep on the same bed afterwards.

Makes more since if one slept on an airbed beforehand, where the definition comes from.

When you eat dirt for the first time and leave your family to build a shack in the woods