Green’s Dictionary of Slang

(Aus./N.Z.) a stupid, foolish person.

1832		Whitehaven Poll Bk 34: He looks parlish like a ning-nang, ; but I hear foke say he's a decent, quietish, hevvy-heedit, sponsihle kind of an auld ninnyhammer.
1908		Maitland Dly Mercury (NSW) 9 Oct. 5/4: He made a great hit throughout the piece, as the silly ning-nang, while his song `The British Aristocracy' was capitably rendered.
1908		Eve. Teleg. (Charters Towers, Qld) 2 Sept. 4/5: There is a suggestion of a plot running through the play - that is a plot on the part of an impecunious lord to marry his son, a rev. gentleman - a sort of ning-nang silly josser - to a ward in chancery.
1919		Smith’s Wkly (Sydney) 24 May 20/1: To boom the show he offered a fiver for the definition of ‘Ning-Nong,’ but nobody collected. The reference was to a peer’s waster son being called a ‘nlng-nong’ by one of the gay girls.
1957		‘Nino Culotta’ They’re a Weird Mob (1958) 15: Gawd I’ve been drivin’ this bloody thing since one o’bloody clock this mornin’ an’ now it’s bloody near time for lunch an’ I ’ave ter get landed with a bloody ning nong who doesn’t know where he’s bloody goin’.
1963–74		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 35: I feel a real ning-nong in this sheilah type frock.
1973		Aus. Women’s Wkly 1 Aug. 31/1: Don’t be misled by this [...] vague air. Virgo is no ning-nong.
1977		(con. 1941) R. Beilby Gunner 108: The only bloody thing worth having in this grab-bag and you trigger-happy ning-nongs blow the arse out of it.
1988		McGill Dict. of Kiwi Sl. 76/1: ningnong idiot, in variation of Northern English dialect ‘ning-nang’; also a worthless person or horse.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].