逆鱗

From Han Feizi, Chapter 12 (《韓非子·說難》):

夫龍之為虫也，柔可狎而騎也；然其喉下有逆鱗徑尺，若人有嬰之者，則必殺人。人主亦有逆鱗，說者能無嬰人主之逆鱗，則幾矣。 [Classical Chinese, trad.]

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夫龙之为虫也，柔可狎而骑也；然其喉下有逆鳞径尺，若人有婴之者，则必杀人。人主亦有逆鳞，说者能无婴人主之逆鳞，则几矣。 [Classical Chinese, simp.]

From: Han Feizi, circa 2^nd century BCE

Fú lóng zhī wéi chóng yě, róu kě xiá ér qí yě; rán qí hóu xià yǒu nìlín jìng chǐ, ruò rén yǒu yīng zhī zhě, zé bì shārén. Rénzhǔ yì yǒu nìlín, shuì zhě néng wú yīng rénzhǔ zhī nìlín, zé jī yǐ. [Pinyin]

The dragon, being a creature, may be tamed, played with in close quarters, and even ridden. However, below its throat are the inverted scales, each spanning one chi. The dragon would kill anyone touching them. A prince of men has those inverted scales too. Persuaders might have a chance at success, provided that they can avoid touching the inverted scales of the prince.

逆鱗

1. (figurative) personal grievance; trigger; pet peeve; taboo topic (especially that of a powerful person)

• tickle the dragon's tail

From the legend in Han Feizi of a scale (鱗) under a dragon's chin that grows backwards (逆) and causes the dragon to enter a fit of rage if touched.

• (Tokyo) げきりん [gèkíríń] (Heiban – [0])^[1]
• IPA^(key): [ɡe̞kʲiɾʲĩɴ]

逆(げき)鱗(りん) • (gekirin) 

1. the anger of a superior

• 逆鱗(げきりん)に触(ふ)れる (gekirin ni fureru)