says Robert Downey Jr. kept "giving him s**t" on the set of 'Tropic Thunder'.
The actor and director says Robert - who stars as Oscar-winning actor Kirk Lazurus, who has his skin surgically altered to play a black man - criticised him for his directorial style.
Ben said: "I did not want to f**k up my Robert Downey Jr. experience.
"But Downey would give me s**t when we were shooting, in a funny, good natured way. I'd be, 'He's making fun of me for doing so many takes. Oh God!'
"But it's clear how much he respects the process. He's always been so funny, so this is not new territory, just new context."
The 42-year-old star also said how touched he was when funny man Jack Black
agreed to be in the film.
He added to Esquire magazine: "I never thought he'd do it. It warmed my heart. I just wanted him to have a good time.
"I wanted those guys to like me, but that's at odds with me being a director."