to have a sharp tongue but a soft heart; describing someone who speaks harshly but is actually kind-hearted

to detest someone or something to the utmost extreme; literally meaning to gnash one's teeth in a way that breaks the heart

to have a sharp tongue but a kind and soft heart (variant form)

To speak harshly or sharply but actually have a kind heart; implies someone whose bark is worse than their bite

Literally "knife mouth but bean curd heart"; describes someone who has a sharp tongue but conceals a soft and caring heart.