This is a phrase used in counter-strike or any type of PvP / FPS / RTS
game. It is used to taunt your opponent when you have either landed an amazing head shot, double kill, or completely
owned a bunch of noobs.
Term came to light on the well known tube video 'mad cause
im stylin', where a rap battle took place and the
guy who used the line got socked in the face.
Basically, it is used to anger your opponent and declare your dominance.