A proverb that is common enough here and whose origin I'm not aware of, literally goes like:
If you are a cock, crow aloud at daybreak; and if you are a hen, then lay your egg and shut up!
I would use it, for example, on an arrogant person who promises to destroy me. It goes along the lines of "if you are a real man, show us what you can do, or else shut up." How can I express this idea, preferably with an idiom or proverb, in English?