It was the jokey serious guy meeting the serious jokey guy: ex-local junkie/journalist David Carr versus the indefatigably in-character Stephen Colbert.

Carr, whose new investigative memoir "Night of the Gun" has become omnipresent, looked nervous at first, even a little constipated, in last night's "Colbert Report" appearance. Carr can effect a faux gravitas that's especially risky around a guy experienced at puncturing real gravitas.

(Disclaimer, David's an old pal, our complicated friendship is briefly in the book, and I never would've caught the segment if our mutual buddy Brian Lambert hadn't flagged it yesterday.)

Carr didn't really play along with Colbert's first question: "You are a former crack addict, and you are a reporter for the New York Times. Which of these two do you think is more damaging to society?"

Refusing to throw his employer under the bus, even for a moment of quippery, Carr soberly defended his craft, adding with no small amount of gravitas, "Using crack cocaine is an idiotic activity that will eventually result in mania and death."

The Colbert question that broke the ice: "You investigate your own life here. You approached yourself as a reporter. Did you get an exclusive?"

Carr, smiling broadly now: "It's funny, but there was not a lot of competition for my life story."

Eventually — as he has done with friends and sources for 25 years — Carr's Nouveau Beat patois broke down Colbert's defenses; at about the 3:45 mark, a drily delivered Carr counterpunch catches the infrequently glass-jawed host with nothing to say. (I won't spoil it for you.)

Other quips, familiar to pals, glistened a bit brighter in Colbert's fun house mirror:

Carr: "I'm capable of imitating a human being for sustained spurts."

Colbert, deadpan: "I know the feeling."

There's lots of other good stuff. The water-cooler factor alone makes it worth six minutes of your Net surfing screw-off time.