Mmmm....the Aussie humour. I agree that it is definitely lame, and people laugh at the lameness. What age group are you talking about? The stuff that my baby boomer parents and their friends laugh about when gathered socially, I think is dumb, like an incredibly lame effort at humour; which I call 'old-man humour'. The sort of humour that makes me shudder inside when I feel obligated to smile and give a half-laugh.
But Aussie humour like Kath and Kim and movies such as The Castle, I think is hilarious.

When I am with my friends we laugh at a lot of in-jokes that seem to continue for months or even years, so to anybody else listening in, Australian or not, they won't understand why we suddenly start laugh hysterically.

Have you read the Bill Bryson book "Down Under", I suggest you do. Also, a tiny book called "Xenophobe's guide to the Aussies" is quite spot-on. Despite what the title suggests, it is actually a light-hearted take on Australians. They have a series on different countries.

This is what it says about the Aussie humour:
"To live in Australia, Aussies have to have a sense of humour. It's a cheap form of entertainment and helps pass the time. Their sardonic and laconic attitude creeps into every conversation. If you display any form of weakness they will tear at it like a dog with a bone.
This irreverent and ruthless lot will aim their jokes at any country and people with any advantage or disadvantage. This is not a back-stabbing population. They will tell anti-English jokes to the English, anti-Irish jokes to the Irish and Ethiopian jokes to anorexics. .....The Aussies can laugh at themselves but of course, with their isolation they have often had little choice. But beware, they don't care for outsiders to do it."