刀子嘴,豆腐心

dāo zi zuǐ , dòu fu xīn

to have a sharp tongue but a soft heart (idiom)

dāo

knife; blade; single-edged sword; cutlass (CL:把[ba3])

zi

noun suffix, as in 椅子[yi3 zi5] "chair"

zuǐ

mouth

,

dòu

legume; pulse; bean; pea (CL:顆|颗[ke1],粒[li4])

fu

decay

xīn

heart