(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. Sue may be intimidating, but that's just because she has to keep a whole department in line. You'll see soon enough that her bark is worse than her bite.

bark is worse than one's bite

One sounds much fiercer than one actually is. Listed in the Oxford Dictionary of Proverbs, this saying dates back at least to the mid-seventeenth century and is used often enough to be a cliché.