We have a friend who often says g'day. He is a gay and most gays don't say g'day. My Tradie Brother and ABI Brother both say g'day. I use g'day advisedly at work. Some you say g'day to, some you don't. Can I explain who I say g'day to or who I say some other greeting to? I cannot. I have grown up with g'day. I suppose I use it appropriately and instinctively. Some people around the highrise, younger males, I might say g'day to. I would certainly not say it to a female stranger or a man dressed in suit. There is no conscious thought about it on my part.
More than once an Indian resident in Australia, probably visiting students, have said to me, good day mate, with perfect diction and a heavy accent. Nah, doesn't work at all. I smiled inwardly. Their cultural educators have done a bad.
Dina in the US has been musing over the use of g'day, I think it is a word best left native Australian speakers. It is not that we mind or care that much, but it just won't sound right. Best to use your own greeting term. We are very used to hearing American greeting terms via our televisions and movies.
The Brits and Irish don't care. They just greet us as they would someone at home. European visitors to Australia are inclined to be more formal.
While there are greeting terms that I don't use, there are a lot that I do. Why do we have so many ways to greet someone?
Really though, it doesn't matter. Being friendly and saying whatever form of hello you choose is nice.