I'd have thought that one of the most common "Australianisms" is not knowing the words to the national anthem.
I still don't know the word to Advance Australia Fair. But I can sing most of Waltzing Mathilda to you!
Just as an aside though, one of my mates over here said to me that when he was growing up, his sporting heros were Dennis Lilley and Jeff Thompson. I cracked up at the time. But thinking on it, who did the Poms have apart from "Beefy"? And he was regarded as an Aussie by the OZ cricket team!