On Wednesday, a day after O'Brien said he wasn't willing to move the "Tonight" show back a half-hour to make way for Leno, there was a certain bite to some monologue jokes by each man.
Leno noted his colleague's complaint that his NBC bosses gave him only seven months to establish himself at the "Tonight" show.
"Seven months!" Leno said. "How did he get that deal? We only got four."
O'Brien returned volley in his own monologue. He said hosting the "Tonight" show has been the fulfillment of a lifelong dream.
"And I just want to say to the kids out there watching: You can do anything you want in life," he said. "Unless Jay Leno wants to do it, too."
Could David Letterman sense something from all the way across the country in New York?
"Isn't it lousy cold outside today?" Letterman said on CBS' "Late Show." "You know, they say, from the weather bureau, they say it's caused by an Arctic chill between Jay and Conan."
NBC still hasn't commented on O'Brien's refusal to play ball, and a negotiated exit seems likely.
Meanwhile, a study emerged Wednesday illustrating just how damaging Leno's prime-time show was to NBC's local stations.
The research firm Harmelin Media said local NBC stations saw their late news audience drop by an average of 25 percent in November compared with the previous year among 25-to 54-year-old viewers. That's the demographic upon which news advertising rates are based.
The decline was particularly steep in some of the largest markets: 48 percent in New York, 43 percent in Los Angeles and 47 percent in Philadelphia.
NBC cited concerns among its 210 local stations in ditching the weeknight experiment of "The Jay Leno Show" at 10 p.m. The network wants to move Leno back to 11:35 for a half-hour show.
The local stations blame Leno for their news ratings going down because he provide a lousy "lead-in," which is television terminology for people keeping their TV set on one station because they were watching something there previously.
Plenty of factors can go into a ratings decline. But Bernie Shimkus, Harmelin's vice president of research, said the decline coincided with the launch of Leno's show last fall. He said he was surprised that the declines were so uniform across the country.
"We all knew it was going to go down," Shimkus said. "But I don't think anyone forecast anything in the neighborhood of 40 to 50 percent."
Harmelin used data on the number of ads run in late local news programs and their cost to calculate that over a three-month period, the Leno experiment would cost these stations collectively $22 million. The 10 stations that NBC owns and operates would lose something like $570,000 per week, the report said.