The line comes from the American sitcom Diff'rent Strokes, which ran from 1978 to 1986, where Gary Coleman played Arnold Jackson and made the question to his older brother Willis a signature catchphrase. Repeated in episodes and later in reruns, clips and compilations, it became shorthand for disbelief long before short-form video existed. Online creators revived it as a reaction sound because the delivery is instantly recognisable even without context, and it still appears in memes, edits and streams whenever someone wants to question a wild claim.