落井下石

luòjǐngxiàshí
  1. to throw stones at sb who has fallen down a well (idiom)
  2. to hit a person when he's down

CEDICT

to kick someone when they are down

Wiktionary

本指別人掉入陷阱或井中，不但不相救，反而向他投擲石塊。語本唐．韓愈〈柳子厚墓誌銘〉：「落陷阱不一引手救，反擠之，又下石焉者，皆是也。」比喻乘人危難時，加以陷害。如：「只有那心術不正的人，才會落井下石，加害於人。」也作「打落水狗」、「下井投石」。

重編國語辭典

乘人危難時，加以陷害

維基詞典

Entry Composition

1 落 luò
  1. to fall or drop
  2. (of the sun) to set
  3. (of a tide) to go out
  4. to lower
  5. to decline or sink
  6. to lag or fall behind
  7. to fall onto
  8. to rest with
  9. to get or receive
  10. to write down
  11. whereabouts
  12. settlement
2 井下 jǐngxià
  1. underground
  2. in the pit (mining)
3 石 shí
  1. rock
  2. stone
  3. stone inscription
  4. one of the eight categories of ancient musical instruments 八音 bāyīn

Related entries

投井下石 tóujǐngxiàshí
  1. to throw stones at sb who has fallen down a well (idiom)
  2. to hit a person when he's down