Two rules to live by are, don't argue with a man who has a microphone, and don't bite the hand that feeds you.

At NBC, both are being ignored.

Jay Leno, who gets well-paid to tell jokes and interview celebrities as host of NBC's "Tonight Show," has recently turned to his own network's prime-time struggles for material. It started last month when Leno cracked that it's so bad at NBC that "'The Biggest Loser' isn't just a TV show anymore; it's our new motto." He followed that up with this dig: "It's so bad, NBC called Manti Te'o and asked him to bring in some imaginary viewers."

Bob Greenblatt, the chairman of NBC Entertainment, didn't take too kindly to Leno's cracks. He sent the host an email expressing his dissatisfaction with the material. That naturally didn't sit too well with Leno, who fired back that people in his position often poke fun at their own network's foibles.

If Greenblatt was hoping his email to Leno would convince the host to look elsewhere for jokes, he was sadly mistaken. Instead, Leno turned up the volume. During his Tuesday night monologue, Leno talked about a woman who sees everything upside down and then added, "In fact, she thinks NBC is at the top of the ratings."

Normally the spat between Leno and Greenblatt would be dismissed as much ado about nothing. A late-night host taking shots at his network and the network president getting irked is about as newsworthy as a dog biting a man.

But this is going on amid speculation that NBC is debating whether it is time to get Jimmy Fallon, whose show follows Leno at 12:30 a.m. ET, ready to take over as host of NBC's key late-night franchise. Those rumblings come in the wake of ABC's Jimmy Kimmel moving to 11:30 p.m. and making a splash with viewers. While Leno is still in first place with both viewers and the coveted adults 18-49 demographic, he is not as dominant as he once was.

NBC has tried to downplay the Fallon talk. Given its woes in prime time and in the morning (where ABC's "Good Morning Amerca" now beats "Today") this does not seem like the ideal time to tinker with one of the few things working for the network.

Also, let's not forget how NBC fared the last time it tried to replace Leno.

Interestingly, a person close to NBC suggested that it was Leno's camp, in true Machiavellian fashion, that was spreading the Fallon rumors - which started around the time of Greenblatt's email - just to put the network brass on the defense.

At this point, Leno has the upper hand. He's still tops in the ratings. But he's made his point. To continue the attacks won't really serve the audience (the jokes aren't that funny) or score him points with his bosses.

As for Greenblatt, perhaps it'd be best to focus more on fixing NBC's prime time and less on Leno's jokes.