teach your grandmother to suck eggs

teach (one's) grandmother to suck eggs

To try to teach an older person who is wiser and more experienced and worldly than a young person may think. Why are you explaining basic typing to Ethel? Yes, she's 70, but she's been using a computer since before you were born—quit teaching your grandmother to suck eggs.
See also: egg, grandmother, suck, teach

teach your grandmother to suck eggs

BRITISH
If you teach your grandmother to suck eggs, you give advice about a subject to someone who knows more about it than you do. Look, I don't want to teach my grandmother to suck eggs, but haven't you done this the wrong way round? Note: You can also say that you teach your granny to suck eggs. At the risk of teaching my granny to suck eggs, wouldn't it be better to use this pan?
See also: egg, grandmother, suck, teach