Green’s Dictionary of Slang

king billy n.

[rhy. sl. (see adj.) but note King Billy n.]

(N.Z. prison) a general insult: a fool, a failure.

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[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 100/1: king billy (also kid billy) n. an idiot; a ridiculous, incompetent person (see following).