This is the era of ever-shrinking men’s trousers — they are tailored and shorter, tighter and shrunken, too tight and too short. And even occasionally veering into: Pitbull, exactly how are you breathing in those high-waisted white pants?

The look of menswear changes at a snail’s pace, and sometimes it takes years before a not-at-all outlandish idea trickles from the runways to the mass market. But when a fashion idea finally reaches the vast middle ground, it tends to stay a while, putting down roots in the menswear landscape.

Thus we are deep in fashion’s equivalent of an old-growth forest — surrounded by men in aggressively tailored pants.

The ubiquity of this trend, even in offices far away from the expected crucibles of creativity, has some people calling these close-fitting trousers too “tight.” While that is a judgment call, it’s true that the cut of men’s pants — the more fashionable cut, that is — has gotten snugger, much snugger than what it was back when Giorgio Armani’s loose Italian tailoring defined power and President Bill Clinton was wearing roomy Donna Karan suits.

The modern suit, from Saint Laurent to J. Crew, now comes with narrow, flat-front trousers, falling straight without a break, sometimes cropped enough to reveal more than a smidgen of bare ankle. The proportions are particularly noticeable on red carpet celebrities whose suits and tuxedos tend to be custom-tailored to the last millimeter, particularly if that suit is by designer Tom Ford and is worn by the likes of Justin Timberlake, Colin Firth or Bradley Cooper.

Cooper, by the way, caused a media fuss when he wore distractingly tight tuxedo pants to a White House State Dinner. His self-described “crazy-town tight” trousers, he later explained, resulted from having packed on pounds for a film role. His was a fashion faux pas, not a fashion statement.

“A slim-fitting suit should skim the body, not hug it,” warns fashion expert Tim Gunn. “It’s not intended to be a wetsuit!”

On the average man, the popular cut — done right — could most accurately be described as lean. The preference for this style crosses ethnicities and economics. It is embraced by twenty-somethings, as well as men in their 50s.

“I think no matter what, a guy will always look good in tapered pants,” says stylist and GQ contributing editor Brian Coats. “But they shouldn’t be so tight everyone is looking at your jewels.”

Inside joke

Jimmy Fallon, host of “The Tonight Show,” has mocked such shrink-wrapped packaging, most recently with a tight pants smackdown featuring Jennifer Lopez. “Everybody’s talking ’bout my tight pants,” Fallon chirped, as he gyrated in tiny white jeans. “Everybody’s looking at my tight pants.”

Fallon’s joke, however, was accompanied by a knowing nod and no small amount of fashion savvy. He “likes things pretty fitted,” says Coats, who works as his stylist. “He’s super into fashion,” Coats says of Fallon, “but he doesn’t want to look like it.”

In that way, Fallon is like a lot of men. They don’t want to look like they’re trying too hard. The slim-suit is a perfect trend. It’s a way to signify stylishness without a lot of bells and whistles.

Men’s attitudes have changed as well, says Memsor Kamarake, stylist and former fashion director of Vibe magazine. Machismo is no longer about puffing oneself up and taking up as much physical space as possible. At one point, models with 29-inch waists used to ask for 36-inch pants for Vibe photo shoots.

For most men, it took some time to get comfortable with the narrower silhouette. Some guys continue to struggle with it. Coats will sometimes style athletes for GQ — average Joe types, not the fashion cognoscenti like Tyson Chandler or Dwyane Wade — and outfit them in slim-cut jeans. A hovering manager will ring an alarm: You’re wearing skinny jeans!

Too tight?

As the mass market has embraced the leaner silhouette, uncomfortable extremes and just plain bad ideas have come to the fore. For example, there are those who go too far: Men who want their trousers taken in to the last binding inch; those who want a suit jacket with a waistline that fits like a corset.

Mostly though, slim has been good. It has flattered the average man’s physique. But now that this aerodynamic silhouette has been popularized, menswear is moving on. The runways in Europe have been proselytizing the merits of a boxier, looser fit.

But outside niche markets, loose remains a tough sell. “I think slim is just more flattering,” Martinez says. “I see double-breasted on the runway, too. And it gives me shivers in a bad, bad way. I don’t like the boxy look. I can’t see myself moving in that direction.”

Well, at least not now. Menswear moves slowly, but like the rest of fashion, it does eventually move.

“It’ll change again and everyone will be wearing palazzo pants,” says Simon Doonan, creative ambassador of Barneys New York. “And then we’ll be longing for the days of tight pants.”