Rob says, "With acting, I was always so scared."

Robert Pattinson couldn't bring himself to drop his pants on camera for Cosmopolis and admits it is still a struggle for him to always feel completely comfortable.

He told Shortlist magazine: ''Oh man, I was terrified on 'Cosmopolis'. There was a sex scene and I was cringing. The girl was really comfortable with her clothes off - and I'm not. She took all her clothes off and I was just sitting there going, 'Um, I haven't got my 'ball-sack' on.' F**king amazing.''

He wants to have more confidence and now Rob says his new life mantra is ''don't be a pussy''.

The 26-year-old actor - who is dating his 'Twilight Saga' co-star Kristen Stewart - has always been really ''scared'' about his career but is trying to be more daring with his choices as he ages.

He said: ''[My life mantra is] don't be a pussy. Basically, that's the best thing you can ever think. I've had so many occasions in my life where I've acted like a pussy and regretted it. Have you seen that Mike Tyson documentary? That bit where he says he'd defeated the guy before he's walked into the ring, it's the same thing.

''With acting, I was always so scared. But you get to the point where you realize it doesn't matter.''

Will his reluctance to show off his package in Cosmopolis show in his next film?

(Image: WENN)