Veteran rapper Talib Kweli was involved in a hellfire-heated exchange with security guards backstage at his Black Star concert last Saturday -- and TMZ Hip Hop has the explosive exchange all on tape!!! The scene opens with Kweli barking at the top of his lungs at a group of men behind the curtain, demanding they tell him "Who the f*** they think they are!!!" According to the sounds of the argument, Kweli was royally pissed off that security guards had walked onto the stage 1 minute past the