The line comes from Monty Python's Flying Circus, where the Spanish Inquisition sketch first appeared in 1970 and became one of the troupe's most repeated running jokes. In the sketch, the inquisitors repeatedly burst into ordinary scenes unannounced, always insisting that nobody expects them, which turned the phrase into shorthand for any surprise intrusion. It spread through television reruns, comedy compilations and later internet memes, where the audio alone instantly signals an ambush. Its staying power comes from that simple, reusable setup.