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When you've had sex with one person in a household and then on another occasion, have sex with another person of the same household, possibly with or without the knowledge of the two parties. Not to be confused with an actual threesome.
Example 1: "So then I walked into his apartment and realized, 'Shoot, I've been here before. I was here last when I was hooking up with his roommate.'" Example 2: "So the two of them actually know each other." "Damn, roommate sex."
by keneticmotion December 05, 2013
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