The TBS late-night comedian played "Plead the Fifth" with Andy Cohen on "Watch What Happens Live" Tuesday night, and was happy to oblige the Bravo host's question inquiring who was the worst guest he's ever had in his decades-long career.
"I don't wanna plead the fifth on anything. Al Roker. The guy...it's too fake. He's too happy all the time," O'Brien said. "And I kept trying to crack him. I said, 'Al, you can talk to me.' And he wouldn't do it! And he goes home at night and cries. It's Roker, I tell ya. It's Roker."
O'Brien also said the "Today" show host was the biggest backstage diva he's ever encountered.
"Absolute monster behind the scenes. Compensating for his own insecurities. And I haven't spoken to him since! Your turn," O'Brien said to Cohen.
"Mine is Mariah Carey, and I think it's a good thing. I mean, look, she had me switch seats because she has a better side. She was a diva in the way that I would want her to be a diva," the "WWHL" host responded.
Two other interesting bits from Cohen's signature game:
Q: Shag Marry Kill: Late-Night James Edition - Jimmy Kimmel, Jimmy Fallon, James Corden
A: "You gotta shag Corden. I don't wanna kill anybody, but I'm going to marry Fallon. He's just a good date. And then Kimmel - I see him around. I know the guy. I know he won't take it personally. So I'm gonna kill that guy for stealing. He stole my beard. I had a beard once, and then he took my beard, so I'm gonna kill that guy.
Q: You are seated next to Jay Leno on a flight. What do you say to him?
A: "Oh, for God's sake. I'm watching a movie. My headphones are on. I don't think we actually talk because I'm so wrapped up in the movie. It's such a good movie that I'm watching. I'm watching 'The Goonies.' And I'm so happy, I don't see who's next to me, and I miss a glorious chance to talk to that wonderful fellow."