Green’s Dictionary of Slang

(Aus.) eccentric, crazy.

1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: dingbat. [...] used in the plural to indicate that the person referred to had ‘rats’ or was not speaking or acting in a rational manner.
1937–84		Partridge DSUE.
1940		H. Drake-Brockman Hot Gold I ii: The poor dope musta been dingbats if he wasn’t poking borak.
1950		Bulletin (Sydney) 13 Sept. 13/3: ‘Dingbats,’ nodded Hal. ‘Been livin’ out with ol’ Bill too long, I bet.’.
1968		D. O’Grady Bottle of Sandwiches 140: Aw, don’t be dingbats. Crocs can’t climb trees.
1974		D. Ireland Burn 47: Walking? You’re dingbats.
1983		Weekend Australian Mag. (Sydney) 27 Aug. 20/8: Australian slanguage is well stocked with words and phrases to describe those who are a bit slow off the mental mark... Not the full quid. Mad as cut snakes. Dingbats, in fact [AND].
1992		R. Park Fence Around the Cuckoo 115: They say they’ll take over the world. Dingbats.