1) RAWK is used to express joy, as in a rallying cry. 2) It can also mean congratulations.
RAWK is the slang spelling of ROCK, originally used by metal fans.
Quite often, it's used to parody (and self-parody) the hard-core fan.
rawks my sawks!
rawkus! (used like awesome)
rawkfist ("rock fist" - forefinger and pinky straight up and your other fingers down, with your thumb over them)
Let's RAWK! You RAWK! We RAWK! I RAWK!