班门弄斧 (Bān mén nòng fŭ), literally “using an axe outside Bān’s door” is an idiom used to remind people not to overestimate their own abilities.
Master Lŭ Bān was an expert craftsman in ancient times, and everyone knew he was the best.
One day, a young carpenter came along, flaunting his hatchet and telling everyone how great he was at building things. A passer-by with a sense of humor asked if the young carpenter could make a nice, wooden door like “that one”, indicating Lŭ Bān’s door. The carpenter was cocky – until he heard whose door it was, at which point his face turned red and he suddenly had important business elsewhere…
The phrase can be used to show respect to someone, like “me doing X in front of you would be like using an axe outside Bān’s door” (so, like, don’t mind me, ok?)
When you realize you've been swinging your axe outside the wrong guy's door. Wikimedia Commons