Fwacha
The grandest of grand of all random exclamations, denoting the general "awesomeness" of the current situation one finds oneself in; although as exclamations often go, it can be used in just about any social situation.
J: "G'day, I got off a perfect score on my SATs, won the lottery and found a heads-up penny on the side-walk."
T: "Fwacha!"
T: "Fwacha!"