Jude Law went shopping this week in a T-shirt that barely contained his huge chest. When, and why, did men start brazenly displaying their hairy cleavage—and wouldn't modesty be better?

Guys, let's talk. How low is too low?

When Jude Law went grocery shopping on Monday, a momentous "he-vage" (that's the meeting point of "he" and "cleavage") event unfolded, captured by the Daily Mail. Behold the flimsy T-shirt barely containing the tufty swathe of hair dusting Law's pecs, and a large chest so defined and unyielding it deserves its own ZIP code.

The deep-necked T-shirt is a dangerous item of clothing for a man. There is only one thing it's good for, and that is a visual hammer-blow to focus attention on a manly chest, a dead-aimed bullseye boast for the breasts, an in-yer-face whoop for a studly rack. If you're brave enough to bare this much flesh—and chest hair, if you have it—the cleft in the chest should ideally be deep, the pecs firmly encased on either side of the V-neck.

Law, 41, has set the "he-vage" bar high, or low, for this summer. There, as he cradles his yellow tomato, is the butch ideal some men have been working towards all those long, cold winter nights, as the sound of Euro dance hits echoed tinnily in their gyms.

The problem, as the comments below the Mail piece reveal, is that no-one will own up to finding the look that attractive. The bitchiest, and best, remark from a reader, about Law is: "Someone tell him he grabbed his sister's blouse by mistake." Women particularly don't seem that turned on by it, no matter how impressive Law's body may be: the most common objection is that the sight of too-obvious "he-vage" takes pride in one's appearance onto the rockier shores of embarrassingly peacockish display.

John Jannuzzi, senior digital editor at GQ, observed Law's public pec display with alarm. "This is, like, too much. Don't let the V-neck fall too far south of the clavicle. A good measure is the V should end four to five inches below a regular crew-neck. If it crosses the nipple line, as it has here, you've gone too far."

But Law is not alone. The streets are teeming with barely-contained chests. Simon Cowell is a he-vage veteran, particularly adept at working the triple combination of deep tan, hairy chest, and crisp white shirt. His predecessors in the seventies and eighties similarly had no shame. The Dukes of Hazzard were masters of button-popped shirts, teasingly open. Elvis's exposed chest came specially encased by diamante-encrusted jumpsuits. Tom Selleck knew the only way to wear a Hawaiian shirt during his Magnum, P.I. years was open, while Burt Reynolds, on the rare occasion his hairy chest was to be found in a shirt, preferred that shirt to be open to the world. The singer Tom Jones growled hits like "Delilah" with shirts sweatily slashed to the navel.

"It's a slippery slope with these T-shirts. When the V gets too deep, you start to see things best left in the bedroom."

The sheer numbers of low-cut V-neck T-shirts on sale shows that men today also want to display themselves. Perhaps it's a symptom of metrosexuality, that sea of self-aware narcissism and gay-appropriated aesthetic display, as perceptively first defined by the writer Mark Simpson. Perhaps all-pervasive body culture is consuming us, male and female, and the low-cut V is—like the sheath dress for women—its obvious manifestation. A survey of British men by clothing store Debenhams found that 75 percent said that they regularly wear their shirt with three buttons undone when out on the town with friends; 41 percent of men will go as far as to risk going four buttons.

Before you attempt this risky fashion move, you need to attain the chest necessary to fill out even the most modest of V-necks. Michael Steinbrick, a personal trainer with New York Sports Clubs, suggests four chest exercises: a chest press, a chest in-cline, a de-cline, and "fly" movement. Work until your muscles are fatigued, says Steinbrick (reality: you're weeping "no more, please, no more"), and do it only one day a week. The de-cline chest exercise will particularly work the lower part of the chest to make "a nice ridge" for the V-neck's base.

The trend for guys in the last few years, says Steinbrick, has been a lean, muscled, swimmer's-build body, rather than the hulky, pneumatic muscle man, "which is a look older guys like."

Jannuzzi still advises caution. "One of the biggest problems in wearing a V-neck is chest hair. The deeper the V, the more chest hair is exposed, and you don't want to be throwing that in people's faces over lunch," he says. "It's a slippery slope with these T-shirts. When the V gets too deep, you start to see things best left in the bedroom. It's better to go with a regular V-neck, and not end up with something too cleavage-y."

Ryan Gosling, as in most things, shows the only sane, reasonable, and handsome way forward, by choosing a V-neck that isn't too showy to induce an avert-the-eyes blush, but low enough still to tantalize.

Gosling is just as adept at wearing what Jannuzzi says is the next trend for summer: the tank-top. This article of clothing is no less fraught a purchase than the low V-neck, of course. Instead of the chest, it focuses attention on the shoulders and arms—which, for exhausted and angsty gym rats, may just amount to swapping one body-shape poisoned chalice for another.