says who

says who or says you  {v. phr.},  {slang}
I don't believe or accept that. — An expression of rebuff often used to make fun of someone or oppose him.
"I am the strongest boy on the block." "Says you."
"That brook is full of trout." "Says who? I never saw anybody catch trout there."
"You can't take Mary to the party — she's my girl." "Says who?"
Categories: {slang} {v. phr.}