Datsun 120Y
I've come across many Australian girls with a "Sunny" disposition (ha, ha). I suppose it depends upon the way you treat them but that can be said of girls of all nationalities - treat them in a boorish manner and you'll get "attitude". Perhaps you just didn't meet the right Australian girl.
STP
Oh, by the way. Did you mean your encounters with Australian girls scared you, as in frightened you, or scarred you, as in left an indelible mark?