Open one eye, close one eye.

睜隻眼閉隻眼
[Pin Yin] Zheng1 Zhi1 Yan3 Bi4 Zhi1 Yan3

To pretend to know nothing about something unethical or improper.

Imagine this face: when you open one eye and close when eye, it's like you are appeasing something you have known. You may use this slang when you beg someone to forgive: "Please open one eye and close one eye. (請您睜隻眼閉隻眼吧！)"

[Example]
她對丈夫的外遇睜隻眼閉隻眼。
She pretend not to know about her husband's illegal love affair.