班門弄斧【ban men nong fu】 是指在行家面前賣弄本領，不自量力不知深浅的意思。
There was a poet called Li Bai in the Tang Dynasty. His poems are passionate, beautiful, and very imaginative. He was know as the God of Poetry. But unfortunately one day he falls into a river and was drowned at Caishiji. To commemorate him, people set up a tomb stone at his grave side.
A man, called Mei Zhihuan, comes to pay his tribute. He thought, “ Li Bai was a great respected poet. I’m really excited to his tomb and commemorate him today!” When he walked up to the tombstone, he saw a bunch of writing on it, “ Oh! What are all those?! They are actually poems . But all of them were poorly handwritten and vulgar in content! These people were so naïve! They thought writing poems on this tombstone would enable their names to be remembered forever like Li Bai!? But how could they have Li Bai’s state of mind?! They were so naïve! They were virtually wielding axes infront of the ancient carpenter Lu Ban, showing off their skills! They were so crazy!!!!!”
Therefore, he composes an impromptu poem:
A tomb near Caishiji River marks the everlasting fame of Li Bai; To and From, every passer-by writes a poem on the tombstone just like a poor carpenter trying to show off his proficiency with the axe before Lu Ban.
【ban men nong fu】 display one’s slight skill before an expert; be conceited; display one’s incompetence before a connoisseur;