Gonzo, you have no idea. I can imagine a lot of foreigners being offended. But all you need to know is:

"Yeah nah" Means no
"Nah yeah" Means yes

"Oi, you're a mad c*nt, aye?" - If said in a happy tone, that's good.
"Oi, you're a mad c*nt, aye." - If not posed as a question and said flatly, that's bad.

This has been Australian 101.