it means motherf*cker...and its being overused by many Indian players when they get killed.. they say like "bc, mc ,mkc" (cursing sister,mother) and it is usual thing in Indian servers, which i don't understand as i don't speak Hindi..and, people don't take it seriously.

And btw, KS Killer is is stupid nub who uses a auto sniper.. Just ignore that guy and have fun.