bark worse than one's bite
bark worse than one's bite {informal}
Sound or speech more frightening or worse than your actions.
The small dog barks savagely, but his bark is worse than his bite.
The boss sometimes talks roughly to the men, but they know that his bark is worse than his bite.
She was always scolding her children, but they knew her bark was worse than her bite.
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Source: A Dictionary of American Idioms