PEPSI is an acronym that stands for: Powerful Ejaculation Produced by Strained Intercourse". PEPSI is used to sum up a sexual experience that spurred amazing pleasure. Although it's common use is to exclaim pleasure or satisfaction so great, it's comparable to an orgasm.
Kelly: Oh my god, last night was amazing!
Emily: So he...(interrupted)
Kelly: Totally Gave me a PEPSI!!!!!
(Below)More Common Use.
Sarah: There's no room in the car, Kelly's gonna have to sit on your lap on the way there.
Timmy: Oh my god, PEPSI.