If a person says I was not born yesterday it means they understand what is really going on and will not be tricked.
The phrase became common in American English in the early 1900s. It plays on the idea that someone born yesterday would have no experience of the world and would believe anything they were told.
The phrase became common in American English in the early 1900s. It plays on the idea that someone born yesterday would have no experience of the world and would believe anything they were told.
Do you really expect me to believe that story? I wasn't born yesterday.