Green’s Dictionary of Slang

(Aus.) an utter fool.

1919		W.H. Downing Digger Dialects 8: andy mcnoon — An unqualified idiot.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: andey mcnoon. An unqualified idiot. From the Arabic ‘Inta machnoon’ – a dammed [sic] fool.