老虎屁股摸不得 (Lǎohǔ pìgu mō bu dé)

Literally: You can't touch a tiger's butt

Example: “经理心情不好，老虎屁股摸不得，今天别提加薪。” — The manager's in a bad mood; let sleeping dogs lie and don't mention a raise today.

English equivalent: Let sleeping dogs lie

Origin: Despite its folksy, timeless-sounding phrasing, the documented origin is considerably more recent and specific than it first appears: Mao Zedong used the exact line in his 1962 speech at the Enlarged Central Work Conference, criticizing officials who refused to tolerate any criticism whatsoever — "won't let people speak, a tiger's rear end that can't be touched; whoever takes this attitude, ten out of ten will fail." Deng Xiaoping later revived the same phrase in a 1977 Central Military Commission meeting, using it to criticize similarly domineering, no-criticism-tolerated behavior within factional disputes. The image itself needs no further explanation: reaching out to touch a tiger anywhere risks a genuinely dangerous reaction, and its rear end is no exception — a vivid warning against provoking someone whose reaction to any perceived challenge is liable to be swift and severe.