- You don't say.
- You don't say.1. Inf. a general response to something that someone has said. (Expresses a little polite surprise or interest, but not disbelief.) •
Bill: I'm starting work on a new job next Monday. Bob: You don't say.
•Sally: The Jones boys are keeping a pet snake. Alice: You don't say.
2. Inf. You have just said something that everybody already knows. •Bill: I think I'm beginning to put on a little weight. Jane: You don't say.
•John: My goodness, prices are getting high. Sue: You don't say.
Dictionary of American idioms. 2013.