Coward! Villain! This is a cockpit phrase; all cocks, except gamecocks, being called dunghills.
“Out, dunghill! dar’st thou brave a nobleman?”
Shakespeare: King John, iv 3.
   That is, Dare you, a dunghill cock, brave a thoroughbred gamecock?  


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from: E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898, found at: Bartleby.com