stands for bad kid basic. refers to players on call of duty 4, and call of duty world at war that do not have a 'turtle beach' or after-market microphone....so their mic is 'basic'. it is not always intended as an insult because most everyone has the standard mic
Johnny: Hahha you fucking suck! I heard you coming around that corner with my turtle beach....bitch!
Ronny: Oh, well I dont have a cool, expensive mic.
Johnny: What a fucking bk basic!