乘人之危
chéng​rén​zhī​wēi HSK7

to take advantage of someone in trouble

  1. 乘 chéng
    to take advantage of
    To avail oneself of an opportunity, circumstances, or someone's weakness.
  2. 人 rén nounpronoun
    other people
    other people; others; another person
  3. 之 zhī particle
    [possessive]
    Connects a describing word or phrase to the noun it describes, similar to 的 de but used in formal or literary writing.
  4. 危 wēi noun
    dangerous
    (bound form) danger; precarious; in jeopardy; to endanger; to imperil