Cf: Bullies are always (generally) cowards (Br.). A bully is always a coward (Am., Br.). The dog without teeth barks the most (Am.). Не threatens who is afraid (Am.). It is one thing to flourish and another to fight (Br.). То flourish is one thing, to fight another (Am.). Those who threaten don't fight (Br.)
Русско-английский словарь пословиц и поговорок. Академик.ру. 2013.