(Go) tell it/that to Sweeney!

dated A scornful or incredulous response to a story or statement that one does not believe or finds ridiculous. Chester: "You know, my dad used to play basketball with the President when they were both kids." Dave: "Ah, go tell it to Sweeney, Chester! Why do you tell such fibs?" A: "I bet you I could eat 20 hot dogs in less than half an hour!" B: "Tell that to Sweeney, pal!" Yeah, right, like you're related to that famous astronaut. Tell it to Sweeney.