Chinese Proverbs -- 刀子嘴，豆腐心

dāo zi zuǐ ，dòu fù xīn　
刀子嘴，豆腐心 

This is a metaphor: the words are as sharp as knives but the heart is as soft as tofu. For example, in the following sentence you can use this proverb.
e.g.
Don’t be nervous, kids, her bark is a lot worse than her bite. She’s really very nice.
她是刀子嘴，豆腐心。