when you are bangin a girl/guy in the dark and you get off and tell them you are going to the bathroom. meantime your buddy is waiting to trade places with you, and your buddy preceeds to go into the room wher the girl/guy was left in the dark and finishes the job. works best if the second person doesn't talk to avoid comprimising the situation.
a.k.a. double dippin, taggin out, or calling the bullpen
dude, that dark swap we pulled last night was brilliant. she never knew it wasn't you when i was bangin her.