My Incomprehensible Aussie Accent

I've had two experiences with my accent drawing bemused stares from shop assistants, so I thought I would write about them here. Funnily enough, most people think I have a very slight accent, and I've frequently been mistaken for American, British and Kiwi. Yet, this sort of exchange still happens:

Me: "I'd like to buy a desk." (standing in the furniture section)
Shop Assistant: "A disk? Erm. I think we have some up front..."
Me: "No, no, a computer desk." (Then, realizing my elaboration would not help) "A desk you would put a computer on."
Shop Assistant: "A disc you would put a computer on...?"
Me: (In frustration) "ONE OF THESE! A DESK!"
Shop Assistant: "Oh! Yeah we sell them."

And yet another classic exchange, this time at a bar:

Me: "I'd like a beer, thanks."
Bargirl: "A bear? Whassat?"
Me: "A beer. You know, BEER." (miming pulling a pint)
Bargirl: I'm not sure I know what that is."
Me: "A BEER! B for Barney, E for Eric, E for Eric, R for Robert!"
Bargirl: "What is it?"
Me: "It's....an alcholic beverage... that people drink at the end of the day..."
Bargirl: "I'll ask the manager what that is."
Me: "OK you go do that."
Bargirl: (After walking 3 paces to her manager, then coming back) "Do you mean a beer?"

Oh man, I hope I never have to communicate anything important to these people.