Cheeky Rhys-Meyers, 28, was shooting a love scene with Johansson when the 21-year-old actress asked him to respect her privacy.
He says, "It was easy work doing the sex scenes. I'd be lying if I said it wasn't.
"I remember Scarlett telling me not to look at her t*ts. And I was trying to be a gentleman and sort of asking for a glimpse.
"But I did sneak a peek. I couldn't help it, they were in my face.
"She has lovely lips and she's a great kisser. Being able to maul her for 30 seconds, I was able to embrace that side of me and the film became easier."