The line comes from Monty Python and the Holy Grail from 1975, during the famous witch trial scene where villagers bring a woman to Sir Bedevere and demand to burn her. The scene parodies medieval superstition, including weighing the accused against a duck to prove she is a witch. Clips of the shout have circulated for years in meme edits, reaction videos and soundboards because the accusation is instantly recognisable and easy to apply to any harmless person who looks vaguely guilty or unusually clever.