Green’s Dictionary of Slang

(Aus.) an idiot, a fool, a general derog. description.

1953		Baker Aus. Speaks vii 171: Nong, a simpleton or fool.
1954		Aus. Women’s Wkly 17 Nov. 40/2: Only local noteworthy contribution is Nong, meaning a drip or a dill.
1959		Baker Drum viii 61: ‘Nong’ (or the duplicated form ‘nong-nong’) was equivalent not only to dill, but also to drube, dope, and drongo.
1960		J. Iggulden Storms of Summer 163: What d’ya expect, ya great nong?
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxvi 4/2: nong: Sometimes nong nong. A stupid person.
1967		J. Wynnum I’m a Jack, All Right 85: Course I remember [...] What d’you take me for — a complete bloody nong?
1976		D. Ireland Glass Canoe (1982) 199: It’s as if they decide you’re a nong and won’t have any part of you.
1979		D. Maitland Breaking Out 59: ‘You fucking nong-nong,’ he rasped.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 37: Nong Nong Fool.
1986		C. Bowles G’DAY 14: Sundy arvo Shane goes down the pub. He meets Gazza. Gazza is a bit of a nong.
1988		McGill Dict. of Kiwi Sl. 77/1: nong idiot; short for ‘ningnong’.
1994		Orsman & Hurley Beaut Little Bk NZ Slang n.p.: It’s a well-known fact that Kiwis have their own way of talking, and without a guide you can easily come a greaser. Have a gink at this beaut little book, and you won't need to feel a nong any more.
1999		G. Seal Lingo 127: One classic Lingoism in this category is nong, a shortened form of ning-nong, derived from British dialect form ‘ning nang’, meaning a fool. nong seems to have burst into general usage during World War II and continues to do good service as a useful expression of doubt about a person’s mental ability.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].
2012		(con. 1943) G.S. Manson Irish Fandango [ebook] ‘[T]ell that poofter priest of yours I’m not gunna be put off by a coupla nongs like you two’.