Somebody's Bark is Worse than his/her Bite

Definition: someone isn't as bad as he/she sounds; someone appears to be worse than he/she is

Explanation: if someone's bark is worse than their bite, they are not as unpleasant as they seem, and their actions are not as bad as their threats 
Examples:

- I wouldn't be scared of her if I were you. Her bark's a lot worse than her bite.

- I soon found out that my new boss' bark was worse than his bite.