First things first, the stereotypes are true and we really do call everyone mate.
But that doesn't mean we like you. Yes, sometimes mate is used in a friendly context, but sometimes it's used as a passive aggressive tool, as in "u fucking wot m8?"
If you really are someone's mate, they'll probably call you "cunt".
Speaking of stereotypes, there are a few things that we really, really don't say. We don't say "shrimp on the barbie". We call shrimps prawns, though we do call barbecues "barbies". Sometimes.
When we say BBQ, we're referring to a) the outdoor cooker and also b) the event of having people round to your place to eat food cooked on the outdoor cooker. "I'm firing up the BBQ for dinner" and "You going to Dazza's BBQ on Sunday?" are both acceptable sentences.
We don't call it a grill, and we don't call it a cookout. Also, "barbecue" doesn't refer to a type of food, like it does in America. If you try to tell an Aussie that a restaurant serves "barbecue food" you'll make a damn fool of yourself.
Also, we don't really say "G'day", unless you're an old mate from the country.
Though, we do swear a lot.
We tend to shorten whatever words we possibly can, usually by adding an "-o" to the end of it.
It's logical, and time-efficient.
Though sometimes we add "-ie". There's no real rhyme or reason to it, just whatever sounds best.
Did you know that an Australian invented the word "selfie"? True story.