He's beloved by the gossip culture of Manhattan and was recently embraced by the left for hurling insults at CNBC "Mad Money" host Jim Cramer. But as Cramer's CNBC "Fast Money" colleagues explained, if you listened to NYU professor Nouriel Roubini, you would have missed out on a lot of stock market upside.

Roubini, often called Dr. Doom and known for crazy parties, predicted back in 2005 the speculative housing bubble would be the eventual undoing of the economy - and he was correct. However, as Jeff Macke, founder and president of Macke Asset Management and panelist on "Fast Money" explained May 11, being two years early with that prediction wasn't something to hang your hat on.

"Let me give you a little hint on trading," Macke said. "If you're two years early on any idea, what you are mostly is dead. You're a professor, as opposed to a trader. And if we still have time to talk after the five-minute butt kissing we gave the guy, I'll tell you what - he hasn't made anyone a cent. Until he does, as far as I'm concerned, it's a nice opinion but it's not making me money."

Once again, someone has squared off against one of CNBC's star personalities, and this time it's a liberal economist taking aim at the old standby, "Mad Money" host Jim Cramer.

An April 8 Associated Press story reported that, on the heels of "The Daily Show" host Jon Stewart taking Cramer "to task for trying to turn finance reporting into a game," New York University Professor and Huffington Post contributor Nouriel Roubini blasted Cramer in an interview. Predictably, Cramer responded.

"Cramer is a buffoon," Roubini said to the AP. "He was one of those who called six times in a row for this bear market rally to be a bull market rally and he got it wrong. And after all this mess and Jon Stewart he should just shut up because he has no shame."