backdoor surprise

v./n. inf(!) to unexpectedly penetrate someone's anus; often, of a heterosexual couple engaged in doggy style intercourse, when the male withdraws from the vagina, and hilariously re-inserts into the anus without prior warning.

NOT to be confused with the equally amusing Cadbury Surprise.

Betty: ... but then, as I... as I was about to... come, for some reason he pulled out... and then... *breaks down sobbing* he.. he put it... oh god! *sobs uncontrolably*
Psychiatrist 1: He gave you a BACKDOOR SURPRISE!? What a guy!!!
*hi-fives Psychiatrist 2*
Psychiatrist 2: Man, that is awesome!

by Terry Deary July 21, 2008

St. Louis Backdoor Surprise

Putting Molly in someone's asshole while fucking.

Popularized in St. Louis by Cardinal fans

She gave me the St. Louis backdoor surprise after the Cardinals' game.

by buttchug32 October 10, 2025