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1.
When two gay men are having anal sex and a third man joins and attempts the anal double penetration, this is called a Nashville Sneak.

This originates from the underground gay scene in 1970's Nashville where closeted country singers were sneaking around in the backs of clubs and hooking up under the radar.
Bert and Ernie were enjoying some good anal sex, then Zack plowed his way in making it a true Nashville Sneak.
by InjectionMachine April 27, 2013