(one's) bark is worse than (one's) bite
One's words or demeanor is worse than one's actual behavior. Mr. Stewart may yell a lot, but his bark is worse than his bite—he's actually helped me carry my groceries many times. Don't worry about Sarah's threats. Her bark is worse than her bite.
your bark is worse than your bite
If someone's bark is worse than their bite, they seem to be much more severe or unfriendly than they really are. My bark is definitely worse than my bite. When people get to know me, they'll tell you I'm just a big softy really.