关公面前耍大刀 – guan1gong1 mian4qian2 shua1 da4dao1
Literal translation – Guangong (name of famous warlord) in front of play sword
Play with a sword in the presence of Guangong
This basically means to attempt to show ones limited skills in the presence of someone who is highly skilled.
Guangong (also known as Guanyu) was a noted excellent swordsman. No one dared challenge him to a sword fight, sort of like a Billy the Kid of Chinese history. So of course if someone was attempting to show their swordsmanship in front of Guanyu it would be embarassing, really, as he would be no match for Guanyu.
I especially like the idioms that encompass a little bit of Chinese culture or history like this one. Any idiom involving Guanyu, Zhugeliang and such figures are all the much more intriguing and interesting in my opinion.
The modern day usage of this proverb I think is pretty obvious. If anyone is trying to flaunt their skills in the presence of someone who’s skills surpass the “flaunter” then this proverb applies.
There are 2 sides to its usage I think. One usage is if perhaps you want to express your humility. If someone is more skilled than you in something but you still carry out the task for whatever reason you can say that you are 关公面前耍大刀 – guan1gong1 mian4qian2 shua1 da4dao1. If you say this in this situation you are guaranteed to get a smile or laugh from your chinese friend. Because you are essentially admitting that they are much better than you at this skill (whatever it may be). So it’s a way to give them a compliment or give them some “face”. Further, a foreigner using an expression like this which is close to their hearts is guaranteed to have an excellent reception.
In a negative way this could also be used to sort of put someone in their place i.e. someone who thinks a little bit too much of themselves because they are limitedly skilled in some area. If someone is in their presence whom is much better then this proverb could be used to humble them or to let them realise they should step aside and let the pro take over.
Another idiom that basically carries the same meaning is 班门弄斧 – ban1men2nong4fu3. The meaning is basically the same, but I much prefer using 关公面前耍大刀 – guan1gong1 mian4qian2 shua1 da4dao1 because of the visual image and the cultural content.