“班门弄斧”，意思是“在鲁班门前舞弄斧子（show off one's proficiency with the axe before Lu Ban， the master carpenter）”。比喻在行家面前卖弄本领，不自量力（show off in the presence of an expert；be conceited），与英文习语“teach one's grandmother (how) to suck eggs”意思相近。

鲁班是中国古代杰出的土木工程师和木匠（outstanding civil engineer and carpenter），他被尊称为土木建筑鼻祖、木匠鼻祖。

例句：

他总是告诉上司怎样经营生意，简直是班门弄斧。

He is always telling the director how to run the business that's like teaching his grandmother to suck eggs.

不要班门弄斧，鲍勃已经打了很多年网球了。

Don't teach your grandmother to suck eggs. Bob has been playing tennis for years.