De Niro wouldn't mind collaborating with rapper 50 Cent off-screen, he says.
"We had some good conversations, and he's a smart guy," De Niro says. "He was very smart about what he was telling me."
(De Niro says he may even try rapping. "You never know," he tells "Extra.")
De Niro also jokes about Matt Damon's weight gain for the comedy "The Informant." He says Damon didn't reach out for advice on packing on the pounds -- even though he famously put on 60 pounds for "Raging Bull."
"He knows how to gain weight. We all know how to gain weight," De Niro says. "It's easy!"
Adds Kirk Jones, the director of De Niro's newest flick, "Everybody's Fine" (out Dec. 4), "Getting it off is the hard part!"