be born yesterday

be born yesterday (no third-person singular simple present, no present participle, simple past was born yesterday, no past participle)

1. (informal, stative, chiefly in the negative) To be new, naive, innocent, inexperienced, or easily deceived.

   Synonym: (US) fall off the turnip truck

   I was not born yesterday, you know. I have done this before!

   • 1840, Henry Cockton, chapter 60, in The Life and Adventures of Valentine Vox, the Ventriloquist, page 508:

     "Do you think," he added, with an ironical grin, "that you'll go for to gammon me into that air! I'm hinnocent, I know, but I wasn't born yesterday exactly."

   • 1915, William MacLeod Raine, chapter 6, in Steve Yeager:

     "Say, do I look like I was born yesterday? See any green in my eye, Cactus Center?"

   • 1998, Gwyn Hyman Rubio, Icy Sparks, page 155:

     "Compared to me, you were born yesterday."

   • 2005, Howard Zinn and Donaldo Pereira Macedo, Howard Zinn on Democratic Education, page 69:

     If you don't know important things about history, then it's as if you were born yesterday.

• Mostly used in the negative to indicate that one is not as naive as had been implied.

• come down in the last shower (NZ, Australian)
• born at night but not last night
• See Thesaurus:naive