"I leave NBC's prime time the way I found it-a total disaster," Leno said.
"I could move to a better business with classier people - like hard-core porn," O'Brien said.
But this afternoon, O'Brien dropped the other shoe - right on NBC's head.
In aO'Brien - who took over the show just seven months ago after five years as Leno's heir - declared: "I cannot participate in what I honestly believe is [the] destruction of 'The Tonight Show.'"
He expressed the hope that he and NBC could resolve their differences "and do a show for a company that values our work."
O'Brien's challenge is the latest blow to NBC, reports CBS News' Jeff Greenfield. Mired in fourth place in primetime, they'd moved Jay Leno to 10 p.m. because his show is far cheaper to produce than scripted drama - some $400,000 per episode compared with $1.2 million for "Law and Order." But the sinking ratings for Leno - 5.3 million viewers compared with the 8 million his predecessors drew - dragged down the late-night newscasts of NBC's affiliates, the source of some 40 percent of the station's revenues.
"The affiliates were screaming," said Washington Post media reporter Howard Kurtz.
And the move cost "The Tonight Show" almost half of its audience - pushing the show into second and even third place behind David Letterman and "Nightline." That's a huge financial blow to NBC - and a blow to one of its key traditions.
NBC invented late-night TV in the middle of the last century. And - from Steve Allen to Jack Paar to Johnny Carson to Leno - NBC has dominated the time slot. The cost of this misadventure - Leno to prime time, O'Brien to "Tonight" - has been estimated at some $200 million.
A host of questions surrounds this latest move by the late-night host. Does Conan's contract allow him to walk away from NBC? Would the network owe him millions if he did? Would he find a home on FOX or in late-night syndication? What seems clearer is that if NBC wanted to make a show out of this train wreck, they could just borrow a title from an old reality show: call it "The Fear Factor."