1.) A practical joke or mischievous act performed during sexual intercourse to the chagrin of one's partner.
2.) An unexpected coital gesture* committed in order to elicit a spook from one's lover.
*Not to be confused with coital jester
ORIGIN early 1980s Youngstown State University, Youngstown, Ohio.
A: So you tricked your girlfriend's parents to hide in her closet?
B: Yeah, I told them it was for a surprise party.
A: And then what happened?
B: I went in there and had sex with her, and her parents didn't know what to do, so they just stayed in that closet.
A: Are you serious?! Then what?
B: I opened the door and yelled "SURPRISE!" No one knew what to do.
A: That's fucked up, man.
B: Sex prank.
A: Are you two still together?
B: No, the relationship ended immediately.