The hotly anticipated summer movie features a passionate kiss between Downey’s superheroic Tony Stark and Paltrow's long-suffering Pepper Potts.
"It was great," said Paltrow, with more than a hint of playful sarcasm in her voice during a press event in Los Angeles Friday, "because both his my husband and his wife were right there on the set."
Despite the presence of Paltrow's hubby, Coldplay frontman Chris Martin, and Downey’s wife Susan, a producer on the film, Downey claimed his costar did not hold back when it came to their make-out scene.
"I couldn’t get her off me," Downey joked. "It was embarrassing!"
But he admits Paltow wasn't entirely pleased with her leading man’s side of the lip-lock. "She said … I didn't know what I was doing, like, 'It didn't feel good.' And I said ‘You know what? First of all, we’re all friends, so what would be creepy is if I was coming off all sexy to you while we were shooting – which by the way, I've done that in movies and it creeps them out! So why would I creep you out?' "
Eventually, Paltrow came around, Downey insisted. "Despite what she said on set, she still thinks about it. "
Downey was not afraid to poke fun at himself – or his past – during the press event also attended by Scarlett Johansson, Don Cheadle, Mickey Rourke and director Jon Favreau. When asked if he'd ever donned a superhero costume for Halloween while growing up, Downey replied "Growing up, no. But in my mid-30s in Palm Springs right before an arrest, yes."