The Twilight star told ShortList that he was scared by a sex scene in David Cronenberg's Cosmopolis.
"Oh man, I was terrified on Cosmopolis," Pattinson said.
"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 added of Cosmopolis: "Normally, you'd think that if you read a script and you don't understand it, you probably shouldn't be doing it.
"But if it's a Cronenberg movie, you have to do it. It was a strange situation. I asked David what it was about and he said, 'I don't know what it's about either'."
Pattinson continued: "I think the script was so bizarre, we thought it was quite funny it was even getting made.
"Literally. It's totally ridiculous. 90% of it is in a limo and it's about getting a haircut and being worried about your asymmetrical prostate.
"It feels like an absolute 'F*ck you' to any kind of hope of commercialism. I'm curious who, if anyone, sees it. It's such a weird movie. I guess, because I'm in it."
Watch a teaser trailer for Cosmopolis below: