Crazy white people who perform hairbrained stunts to impress people, usually frat guys or dropouts. See Jackass
Glen: I don't know, what?
Truman: Dude! Check this shit out!
Usual indicators are found in the ankles and cheeks in particular
(2) To disprove a suspected prinny or flatspot.
"Oh, nothing really. We hung out for a while, I made sure she was satisfied, and we went to sleep."
"Oh man! You FWPed the shit out of her!!"