Viz is right in saying that aggro is written with two Gs, and in that form, it is an allowable Chi word.
It's not specifically Australian. Dictionaries tend to label it as British, but like many words so-labeled, it's widely used in Australia, and probably quite a lot of other countries too. I once saw a guide to Australian speech (compiled by an American who had lived in Australia) that included that quintessentially English word cuppa (cup of tea). I suppose the word belonged in the guide if the aim was to define unfamiliar terms that an American might encounter in Australia.