an Aussie is used when your to lazy to type "Australian". this can also be used in a offensive way depending on the person and if there patriotic of there country or not. the examples will follow below.
using it because your lazy: Hey, look at that Aussie tourist.
using it in a offensive matter: stfu you stupid ass retarded Aussie. you motherfuckers have the lowest iq in all places. go to hell, nvm you guys are already in hell.