The typical map or globe of Earth shows America close to the equator, while Australia is far south. Although this does not technically make Australia “beneath” him, as space has no sense of direction, it does make Australians “beneath” him from an Earth based perspective.

As for “Niggas” being “beneath” him, he probably means this in terms of lyrical skills, reputation, body mass, and many other things as well.
There is a scene in the film “The Street Fighter” in which Sonny Chiba karate-chops another man in the mouth, making him lose all of his teeth. This line is a direct reference to the event within the film.
Anchorman reference.
http://www.youtube.com/watch?v=zLq2-uZd5LY