The act of placing your hand between someones ass
cheeks from behind, and flopping your hand side to side in a manner that resembles a guppy.
One must shout "guppy" before executing the act; Forewarning is necessary to allow the victim time to clench
cheeks and minimize penetration.
(noun) "I let my guard down while
Jennie was behind me and she gave me a guppy."
(
verb) "She guppied me so hard, I'll be walking with a
limp for the next 24 hours."