G'day,

McGrath:
Of course it could be fake folk etymology - but it sounds quite plausible to me.

That's the first hallmark of 'folk etymology'!

There are no citations from written/published sources of this meaning in The Australian National Dictionary, 1988, (which is probably the source of the Australian citations in the latest OED mentioned by Q, as it was a local Oxford project - giving full OED treatment to local Australian words.) The popularity of the later meaning of typical working-class Australian definitely is linked with the Mavis Bramston Show - whch was something of a succès de scandale ... until the Catholic church's threat to sell offr their huge shareholding in Ampol (petrol company - sponsor of MB Show) if they didn't censor the show!

As regards "Hun" as source for "Hoon" I think that unlikely since the 'flash'/'pimp' usages were common here long before the revival of "Hun" for Germans (post-Bismarck - WW 1 ... ?).

Regards,