teach one's grandmother (how) to suck eggs
1. 班门弄斧
He is always telling the director how to run the business; that's like teaching his grandmother to suck eggs.
他老是对总裁说该如何管理业务, 就跟班门弄斧似的。
习惯用语shoot one's grandmother1.[美俚]找错了目标; 扑了一个空, 搞错shoot one's granny1.[美俚]找错了目标; 扑了一个空, 搞错teach one's grandmother (how) to suck eggs1.[英口]教训长辈; 班门弄斧Tell that to your grandmother.1.胡说。This beats my grandmother.1.吓了一跳。