Scrub a dub dub is a playful variation on rub a dub dub, the opening of the traditional English nursery rhyme about three men in a tub that has been retold for generations. The wording shifted over time toward bath and washing contexts, which is why the phrase now appears in children's songs, cartoons and everyday jokes about getting clean. Online, the short spoken version survives as a reaction clip, shared for its instant recognition and for how easily it turns scrubbing, bathing or cleaning footage into a joke.