be born yesterday

Verb

in the negative informal no-past-participle no-present-participle

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

Japanese Meaning

（口語表現、主に否定文で）世間知らずで、経験不足なために容易に騙される性質があること / 新米で、未熟な面があること / 純真で無邪気だが、そのために単純だと見なされる様子

Don't expect me to be born yesterday; I won't fall for that trick.

私を世間知らずだと思わないでください。そんな手には引っかかりません。

Sense（1）

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

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

was born yesterday

（ past ）