teach your grandmother to suck eggs
教奶奶嘬（吸出）鸡蛋；在能人面前逞强；班门弄斧；关公面前耍大刀
to tell or show sb how to do sth that they can already do well, and probably better than you can
这句习语源于1707年John Stevens翻译的《Quevedo's Comical Works》中：
You would have me teach my Grandame to suck Eggs.
比喻在行家面前卖弄本领，不自量力；给别人提出完全没有必要的建议或劝告：请看，
The new employee tried to give me advice on how to handle difficult customers, but I've been working in customer service for years. It's like teaching your grandmother to suck eggs.
新员工试图给我关于如何处理难缠客户的建议，但我在客户服务行业工作多年了。这就像是教你的祖母吸食鸡蛋一样多余。
Do not teach your grandmother to suck eggs.
不要班门弄斧。
Don't try to teach me how to use a computer, I've been working with them for years. It's like teaching your grandmother to suck eggs.
不要试图教我如何使用电脑，我已经用电脑工作多年了。这就像是班门弄斧。
Don't suggest showing Mary how to knit. It will be like teaching your grandmother to suck eggs.
不要建议向玛丽展示如何编织。这将会像是你在班门弄斧。
My friend tried to explain the rules of basketball to me, but I've been playing the sport for a decade. It's like teaching your grandmother to suck eggs.
我的朋友试图向我解释篮球的规则，但我已经打篮球十年了。这就像是关公面前耍大刀一样多余。
The young chef tried to show me how to chop onions properly, but I've been cooking for decades. It's like teaching your grandmother to suck eggs.
年轻的厨师试图向我展示如何正确切洋葱，但我烹饪了几十年了。这如同关公面前耍大刀。
类似表达：
Never offer to teach a fish to swim. 不要班门弄斧。
I don't want to teach fish how to swim before you.
在你面前，我可不敢卖弄。
teach a dog to chase rabbits
teach the Pope how to pray