Try the old "g'day" line at a pub in London now, and at best you'll get a roll of the eyes, at worst a "piss off jafa".
So what's happened to the lovable Aussie?
Firstly, we're suffering from a serious case of overexposure. The fact that Australia is so far away from anywhere else used to mean that not many of us made it to foreign shores. Now, not only do we have air travel, but we have extremely cheap air travel, meaning that any wanker who can manage to scrape together a few hundred dollars can go and prop up the tittie bar industry in Phuket for a week or so.
It also means groups of blokes on buck's weekends can wreak havoc on the world in an "I'm sick of getting pissed at Establishment, let's go do it in Bali" kind of way.
Ah well, not all is lost. If you travel to places where Aussie wankers rarely venture to (say, Central America over South America or Vietnam over Thailand) you can still enjoy yourself overseas without the fear of seeing your fellow country men belting out drunken renditions of Khe Sahn.