戳脊背

chuōjǐbèi ㄔㄨㄛ ㄐㄧˇ ㄅㄟˋ

    • to criticise or gossip about someone behind their back

Character by character

Saying俗语俗語

Idiom惯用语 · Widely known

Literally
poke someone's back
Meaning
A variant of 戳脊梁骨: to criticise or gossip about someone behind their back.

Sources