you don't say|say イディオム
you don't say|say
interj.,
informal 
Used to show surprise at what is said.
Your ring is a real diamond? You don't say! "Bill and Jean are going to get married." "You don't say!" Synonym: DO TELL.
you don't say|say
interj.,
informal 
Used to appearance abruptness at what is said.
Your arena is a absolute diamond? You don't say! "Bill and Jean are activity to get married." "You don't say!" Synonym: DO TELL. Dictionary