Two Close Friends where one of them is is about to or is already screwing some chick/dude, and without the other (3rd party) person knowing, they swap with each other.
The "Bae and Switch"
The Bae and Switch: I was stuck in a room with this fat chick, and I didn't wanna fuck her, so I hit the light, and pulled a Bae and Switch with my Wingman.
When finally finding "the one" or ones "bae for life", one proceeds to tap the bae once on each shoulder with ones dick as a way to claim her for ones own.
Dick: "I spent last nightknighting the bae after she gave me a sweet blowie."
John: "no way man! I'm so jealous! "