If you call Britney Spears a 'fat b****' while she's live on stage, it's her prerogative to respond in kind. <br />The 33-year-old dropped an F-bomb - and an A-bomb - at a man after he heckled her during her Piece Of Me show at Planet Hollywood in Las Vegas on Wednesday night. <br />An Instagram clip uploaded by an audience member shows the moment the singer responded to the barb
