So, here's how it went down, as I listen on Media Matters:
Carville: I'll tell you this. Bob...
Novak: James, just let me finish what I have to say. I know you hate to hear me (during this time, Carville is saying "Wow. Wow. Wow.")
Carville: He's gotta show these right wingers that he's got backbone, y'know. The Wall Street Journal editorial page is watching you. Show 'em you're tough.
Novak: Well I think that's bullshit, and I hate that. Just let it go.
At this point, Novak hesitates for a minute, then puts his hand on the table, then realizes what he's done, then gets up and walks off. So, what was it that set Novak off. Some people have speculated that it was staged because he was going to be asked about Plame. After watching the clip numerous times, I don't think so. Novak gets genuinely angry when Carville mentions the Wall Street Journal editorial page. More likely, I think, is that there is some subtext, some inside knowledge that Carville has (probably from Matalin) and that he sprung on Novak mid-show to produce a reaction. He got it.
Can we speculate on what that inside information could be, just as an exercise? I think it might be something like this: The conservative kooks at the WSJ Editorial Page think Novak rolled over on the Plame leak, and they are shunning him from the conservative social scene. That's why Novak had to come out with that asinine column last week, and that's why Carville says that he has to show them that he's "tough." They think he sang like a bird, so he has to "show these right wingers that he has backbone." It's probably the talk in these elite conservative circles that Novak is a coward and couldn't protect Rove and the President in the face of the Grand Jury investigation. And Novak knows it. This was possibly a sly personal shot at Novak. I don't really see how this seemingly innocuous statement by Carville could have produced such ire and panic for Novak otherwise. He actually looked like he was ready to hit Carville. Very interesting.