The line comes from Tombstone, the 1993 Western about Wyatt Earp and the gunfight at the O.K. Corral, in which Val Kilmer plays the tubercular gambler and gunfighter Doc Holliday. Holliday uses the phrase when volunteering for a fight, and its calm delivery helped make it one of the film's most quoted moments. Clipped from the movie and shared online, it became a favourite reaction sound for challenges and confrontations, and it remains popular because the short clip needs no setup to be understood.