Mickey Mouse first says “Hot dogs” in the 1929 short The Karnival Kid.
The film is notable because it was Mickey’s first speaking role. Earlier Mickey cartoons had used synchronized music and sound effects, but Mickey himself had not spoken dialogue. In the short, he works as a hot-dog seller at a carnival and calls out his product.
The phrase became closely associated with Mickey’s early screen personality and with the sound-era development of the character. It is sometimes confused with Mickey’s first vocal performance overall, because Walt Disney had supplied Mickey’s voice in earlier productions’ songs or vocal effects; The Karnival Kid is specifically remembered for Mickey’s first spoken words.
The short also features the first appearance of Mickey’s elongated, flexible “rubber-hose” tongue, another visual gag from the early Disney style.