When a man reaches around a woman during face to face coitus and spreads her anus, then swinging his testicles into the woman's anus from underneath. The anus is then released at exactly the right time in order to close around one or both of the man's testicles. Often this sex act is accompanied by humming the theme song to the Back to the Future film trilogy.
by SlowMoJones August 24, 2010