Definition of I or he, she, etc. wasn't born yesterday in English:

I (or he, she, etc.) wasn't born yesterday

Used to indicate that one (or another person) is not foolish or gullible.
More example sentences
  • I've heard a few things about these things; I wasn't born yesterday, you know.
  • Mel, I wasn't born yesterday; now go get ready before I change my mind.
  • I understand second guessing, I will do it at times also, but let's use this to remember that Walt wasn't born yesterday.
See parent entry: born

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Pronunciation: ˌəʊlɪˈadʒɪnəs
adjective
rich in, covered with, or producing oil; oily