That's a joke, son!

A brusque, vaudeville-style put-down, the line reads as a comic correction: the speaker insists that what has just been said should be taken as humor, not as a serious claim. In Fred Allen’s persona—wry, self-aware, and often mock-combative with other performers—such a phrase would function as a deflationary tag, puncturing pomposity or stopping an argument by reframing it as mere gag-work. The address “son” adds a note of mock authority and condescension, a common comedic device that heightens the sting while keeping the exchange in the realm of banter.