someone's bark is worse than his/her bite idiom
刀子嘴豆腐心;言语比行动吓人
If someone's bark is worse than their bite, they are not as unpleasant or frightening as they seem.
Don't let her frighten you - her bark is worse than her bite. 别被她吓倒了，她这人是刀子嘴豆腐心。