揭老底

jiēlǎodǐ ㄐㄧㄝ ㄌㄠˇ ㄉㄧˇ

    • to expose someone's past or hidden facts about them

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Saying俗语俗語

Idiom惯用语 · In everyday use

Literally
lift the old bottom
Meaning
To expose someone's past or the hidden facts about them. Usually unwelcome to the person exposed.

Sources