03/27/2008 at 09:00 AM EDT
What happened in Vegas? Don't ask Kate Bosworth
– she can't remember!
The 25-year-old actress cannot recall shooting her love scene with Jim Sturgess for 21
, she told PEOPLE at Wednesday's Cinema Society and Calvin Klein Jeans-sponsored screening of the film in Manhattan.
"We were both so drunk," the Superman Returns
star said. "Jim and I became such good friends, we decided to have a couple of drinks, loosen up and go for it."
Surgess – who plays the lead in the shot-on-location casino flick, based on Ben Mezrich's book, Bringing Down the House: The Inside Story of Six MIT Students Who Took Vegas for Millions
– has similarly fuzzy recollections.
"We were on Grey Goose, I think," said the British actor. "It was brilliant for about half and an hour. As we continued to drink ... it just became sloppy and messy. I couldn't stand up at one point."
After the screening Wednesday, the two stars headed to SoHo's Mercer Kitchen, where Mary-Kate Olsen
, Helena Christensen and Clive Owen joined in for dinner and blackjack.
Unlike in Vegas, everyone was on their best behavior.