Idiom: I (he/she, etc.) wasn’t born
yesterday


Meaning: Something that you say in order to tell someone that
a person is not stupid and cannot be easily deceived

Context #1
Selena:Kelly, this place is a mess! I thought
you were going to clean everything up and decorate it for the party tomorrow.
That is what you told mom.
Kelly: I did! I’ve been cleaning all day long. I
only have a few more things to do. Please back me up on this with mom.
Selena: Seriously?
She wasn’t born yesterday. She knows you’ve just been sitting around
all day watching the whole season of Game
of Thrones again!
Kelly: Well, that show is so addicting. I just
couldn’t stop.
Selena: We might as well finish up here before mom
gets home.

Context #2
Jennifer: Wait a second….Tommy, what is this on your
shirt? It looks like pink lipstick.
Tommy: Huh? Oh no. Is that lipstick? Um….let me
think. When I was on the bus today, a
woman with really high heels stumbled while she was walking down the aisle and
her face fell right on my shirt.
Jennifer: You know what? I wasn’t born yesterday. I’m surprised you couldn’t come up with a
better story than that, cheater!

Meaning: In Context 1, Kelly claims that she cleaned everything up
for her mother, but it is obvious that she hasn’t done anything. Selena tells
Jennifer that her mom will not believe her. In Context 2, Jennifer finds
lipstick on her boyfriend Tommy’s shirt and asks him about it. When he makes up
a crazy story, she tells him she doesn’t believe him and is not stupid by
saying “I wasn’t born yesterday.”