One of the oldest rules in broadcasting (I'm thinking back to my TV anchor days) is that you should always assume that your microphone might be live. Yet time and time again we see that rule violated. And often it comes right at the moment when the commercial break ends.
Bob Beckel was obviously carrying on with an off-air argument and missed any cue about going back live. So he finished yelling at Neil Boortz, "You don't know what the f**k you're talking about."
Update: The initial accounts of Beckel's profanity being targeted at Neil Boortz proved to be incorrect. Beckel's ire was focused on fellow panelist Jennifer Stefano. She recounts the experience here.
Here's the short version courtesy Gateway Pundit:
But it maybe worth watching the longer version.
In a blooper that is as hilarious as it increasingly becomes painful, it slowly dawns on Beckel what actually happened, as Hannity insists he apologize and Beckel, after saying he won’t several times, finally realizes the cameras are actually rolling. When he finally figured it out, he told Hannity to “run your show better,” then covered his head in shame and refused to speak, other than to say “I’m going to be fired.”