Necklines are plunging all over the country. And if left unsupervised, they can be scarier than Nicolette Sheridan in sequins. Men are breaking the two-button rule and freeing the chest hair, flaccid pecs, pale skin, and all. For more genetically blessed gents, it works: Brad Pitt, Hugh Grant, and Jude Law have all mastered the nuances of slick-Rick styling. As has Tom Cruise, who's been coming undone since Risky Business.

They should be thanking another Tom, though, for putting the sex back into the shirt. "Tom Ford carries it off because he's Tom Ford. That's his shtick," says Michael Anderson, vice president of design for menswear at Banana Republic. (Consistency is key—Ford has been letting the air kiss his breast meat for years.) It would also help if you know how to, say, detonate explosives and seduce Catherine Zeta-Jones, like the entire cast of Ocean's Twelve or whoever's going to be the next James Bond. All work better with hard nipples than a tie.

But there are significant differences between matinee idols and you, common man: They're called groomers, personal trainers, year-round tans, and a sense of entitlement. (Even then, there are those who consistently get it wrong—like John Travolta, who still appears to be suffering from the Fever.) "It's a lifestyle," Anderson says. "You can't wear a cardigan one day and then have your shirt undone to your navel the next."

Take it from one who knows: "Very few dudes can pull it off," says Erik Estrada. The CHiPs star who looked so arresting in barely-there khaki knows where to draw the line. "It's got to visually fit. I wore my shirt practically unbuttoned back in the day because that was the era. There was a lot of sex in those days. You had to be ready."

So if you insist on showing a wedge of pecs, leave the starched Oxford and the breezy St. Barts linens in the closet. "When you wear your shirt unbuttoned, it's a snob thing, a class statement," says Tom Kalenderian, executive vice president and men's general-merchandise manager for Barneys New York. Kalenderian suggests a shirt made of cotton poplin or silk crepe, which will gently hang off the body, rather than a starched version that requires a T-shirt underneath as a scratch guard. And if white seems too drab, pick a soft shade like lilac, rose, or baby blue. "When you wear it right, it should be a chic-y thing, not sloppy," says DSquared designer twin Dan Caten. Anderson adds, "Done right, leaving a shirt unbuttoned low is a nod to old haberdashery, like a sixties Michael Caine."

But if a man weighs more than 175 pounds, he should just draw the curtains. "It's a dressed-up sexy without being tight and busty," says Caten, who adds one vital caveat: "No big tits."