Bradley Cooper on Crying, Drugs, and Future 'Hangovers'

March 17, 2011 — -- In "The Hangover," he played the fist-pumping heartthrob, the bad boy with the big hair. But Bradley Cooper's not bent on being a summer blockbuster staple forever. He's got serious acting chops up his sleeve, which he shows off in the psychological thriller "Limitless," in theaters Friday.

That didn't make denigrating his on-screen idol any easier, though.

"I had to stand across from Robert De Niro and call him my b***h," Cooper said in a recent interview with ABC News Now's "Popcorn With Peter Travers."

Cooper stars opposite De Niro as Eddie Morra, a down-on-his-luck writer who takes a mind enhancing drug called NZT.

"What would happen if you took a drug that could open 100 percent of your brain?," Cooper mused. "I'd like to hear the person who wouldn't take it. I want to hear the argument."

NZT allows him to catapult to to top of the financial world, where he meets De Niro's Carl Van Loon, a businessman intent upon making money off of him. For Cooper, De Niro was a fortuitous foil. Years ago, as a student of Pace University's Actors Studio Drama School, he asked De Niro how he got into character for "Awakenings" only to be brushed off by the star.

How things have changed. When Cooper appeared on Monday's edition of "Inside the Actors Studio," host James Lipton played the a clip of the actor in the audience for the De Niro show. It moved Cooper to tears. Actually, he struggled to speak multiple times.

"I'm a loud crier," Cooper told audience at one point (an audience that included actress Renee Zellweger, his girlfriend since 2009). "I'm not like a sobber ... I'm like a -- it's ugly, so I apologize."

"It was way too emotional," he said on "Popcorn." "I kept apologizing to the audience."