*shrug* I dunno...
I have been trying to find a genuine Australian joke for years, so I was cut when I found out that the previous gag wasn't. :(
An Australian told me these ones a few months ago:
Q: What's the Australian idea of safe sex?
A: Painting X's on the backs of the animals that kick.
Q: How is an Australian lover like a wombat?
A: He eats roots, shoots, and leaves.
The first one could be a general joke, but I'm pretty sure that last one is exclusively Australian.