班門弄斧 <to teach someone something that he already knows>
= to teach one’s grandmother to suck eggs <idiom>
= to teach fish how to swim
= to show off in front of an expert
I just gave instruction to him on how to set up a computer. I didn’t realize that he is a computer technician. How embarrassing! It is like teaching fish how to swim.
** 版權所有 - Elisa