Hecklers generally see the chance to illustrate the cutting edge wit they display down the pub each night and pit it against a pro.
always ends in fail for the heckler
Pretty accurate to be honest, hecklers seem to think that stand-up comedy is a two way communication experience, but I think the hint is that only one side has a mic and spotlight!

Jimmy Carr is much much funnier on stage than he is on TV, but its more that he can get away with far more live than is allowed on broadcast.