Howard Stern got Robert Downey, Jr. to open up about his own 50th birthday bash, which was a star-studded celeb event.

Downey told Howard Stern that he had purposely set the event up in such a way that celebs would be comfortable.

“I asked that no one bring cell phones,” Downey told Howard Stern. “We had no cameras. People said that they were able to enjoy themselves like they hadn’t in years because they weren’t worried about someone getting a picture of them dancing.”

As a result of this freedom to be themselves, he says that stars were much more relaxed.

“Reese Witherspoon, she and my agent, who is her husband were there, and she danced all night.”

Two bands played Downey’s birthday, Steely Dan and Duran Duran. The relaxed atmosphere encouraged some Celebs Gone Wild behavior.

“Duran Duran knocked it out of the park. They opened with ‘View To a Kill,'” Downey told Stern. “At one point, I won’t mention who, someone’s wife took off their bra and threw it on stage during Duran Duran.”

Downey told Howard Stern that he was particularly jazzed about Steely Dan. He even got up and sang with them. But he forgot the words!

“I’ve gone to their concerts at the Beacon, just sitting there crying during the songs. I was out of my body. It was a horrible band/fan moment. They had seen me perform it on the Wayne Brady Show seven years ago and thought I had been practicing it ever since.”

Downey explained that he did not push to get on stage with Steely Dan. It was not his idea.

Howard Stern asked, “Was Steely Dan annoyed by you getting up there with them?”

“No, they asked me. I’m also somebody that, if I see a great band or performance, I just want to enjoy it. I’m happy to come on this show (The Howard Stern Show), and I said I would and I’ll do it, and right now I’m cozy, but I would be so happy just to listen to the show forever and never be a guest.”

Other guest A-listers enriched the evening.

“Dustin Hoffman was there, that made my night.

“At one point I was on the floor dancing and I looked over and Edward Norton and Jason Bateman were on the side clowning me, whispering to each other about what a complete douchbag I looked like jumping up and down.”