don't teach your grandmother to suck eggs
don't teach your grandmother to suck eggs
An older person is wiser, more experienced, and more worldly than a young person may think—thus, the older person does not need to be taught by the younger. I may be 70, but I've been using a computer since before you were born! Don't teach your grandmother to suck eggs, sonny!
Farlex Dictionary of Idioms. © 2022 Farlex, Inc, all rights reserved.