At least he had the television smarts to show up during a ratings "sweeps" month.
"This is a live Mardi Gras every morning," Letterman told Philbin and co-host Kelly Ripa.
Letterman showed pictures of son Harry, joking that the 1-year-old was looking at "mom's beer can" in one. He and Philbin traded good-natured gibes about who was most negligent about inviting the other on social occasions.
After Letterman complained that Philbin hadn't invited him to dinner, the stage curtain opened to reveal a table for two, with breakfast steaks set out.
"I want nothing to do with this phony dinner!" Letterman said.
They made some small talk about Notre Dame football, and Philbin tossed in a political question: Why did John Kerry lose?
"Geez, I have no idea," Letterman said. "I know nothing about politics. If I knew anything, why would I be here?"
But the two have an odd chemistry, and the irony-drenched Letterman clearly respects the showbiz veteran Philbin, 73, who's in the Guinness Book of World Records for logging more than 15,000 hours in front of a television camera.
"He is so quick and inventive and imaginative," Philbin told The Associated Press later. "His show is one surprise after another and I admire that tremendously. What does he see in me? I don't know."
Philbin said "Live" had asked Letterman to appear so many times that the show had nearly stopped asking.
"I know how private he is and how much he didn't want to do this," he said. "It was awfully nice of him to come by."
As for a return engagement, don't hold you're breath. That's what Letterman indicated when Philbin asked when he's be back.
"None of us will live that long," he replied.