Top Definition
1.)one penis simultaneously gets off 2 women.
2.) A menage trois.

3.)Having sex with someone then forgeting if you actually had sex.
1.) The magic penis theory. "I shot her in the grassy knoll then I ran away and no one ever found me"
by Michael Doyle June 04, 2003
1 more definition
The theory that any bisexual person just hasn't had the right cock yet. Bisexual woman? She must just be curious but actually straight. Bisexual man? He must just be closeted.
"Amanda and Liz seem so perfect for each other! Any idea why they aren't together?"
"Amanda says she doesn't date straight girls."
"But isn't Liz bi?"
"Yeah, but Amanda still subscribes to the magic penis theory."
by briaguya April 20, 2015

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