Rosario Dawson just wanted to show off boyfriend Jason Lewis to her mom, Isabel. So she popped in a DVD of Lewis as Smith—Kim Cattrall's impossibly gorgeous younger beau—in Sex and the City. "I had no idea you saw his butt in half of it," says Dawson, who has dated the actor, 33, for nearly a year. "My mom is like, 'Your boyfriend has a nice butt.' I said, 'That's it. I'm turning this thing off.' "

Such prudish moments are very rare for the adventurous Dawson, 25. "I am a pretty fearless person," she says. She proves it as an Uzi-toting prostitute in the new film Sin City, in which she sports a mohawk and a barely there leather-and-fishnet ensemble. "She was like, 'Hell yeah, I'll wear it,' " says director Robert Rodriguez. "You have to have a lot of confidence to carry that off." Part Puerto Rican, African-American, Irish, Cuban and Native American, Dawson was discovered while sitting on her New York City stoop at 15 and made her debut in 1995's racy Kids. She has since shined in 1998's He Got Game and 2002's Men in Black II (next up: a film version of the hit musical Rent) and even sees the bright side of going topless in last year's flop Alexander: "In 80 years I will be able to look at that and say, 'I had a pretty nice rack back then.' "