Chances are you've been there: a dinner party where you get stuck sitting next to a lawyer who has nothing to say about the law—but won't shut up about Chamois Butt'r cream and the wonders of his triathlon ladder workout. Your coworker Seth, across the table, presents an iPhone slide show in which he is doing his best impressions of Usain Bolt, Lance Armstrong, and Michael Phelps. And then Steve, the creative director playing host, announces that when he travels for work he books only hotels with pools, so he can get in his lap time. More subtly than, say, whipping out the keys to his Bugatti, a certain sort of image-conscious striver makes the distinction clear: Prestige comes with being an athletic triple threat.

It used to be that only true He-Men dared call themselves triathletes, but now all manner of aspirant, Type-A personalities are trying on the title. These are the guys who put the "try" in triathlete, who've seized on the once-forbidding sport as a form of social currency, the athletic equivalent of dropping mentions of a Hamptons summer home or a Harvard M.B.A.

If you're a mere, uh, uniathlete, step aside. And if you're an actual Ironman, well, you've already been making room for plenty of Johnny-come-latelies: USA Triathlon, the governing body of the sport, counted 53,000 dues-paying members in 2004; last year there were more than double that number. The group estimates that in recent years as many as 250,000 Americans have participated in triathlons annually.

A lot of them, says George Dallam, author of Championship Triathlon Training, are corporate types looking to prove they're insiders: "I think today's executive is just as likely to be a triathlete, whereas 15 or 20 years ago that person would have always been a golfer—golf would have been the way you bonded with other executives." And while Dallam won't knock anything that gets Americans off the couch, he can't help but be nostalgic. "I started back around 1981," he says, "and in those days it was a very bizarre group, probably not more than a few hundred people in the whole country who were actively pursuing triathlon."

Therein lies the paradox of the sport: Even as it has gone soft—with no shortage of pussy races that, for instance, substitute 15 pool laps for multi-mile open-ocean crossings—the triathlon has somehow held on to much of its cred. "In the early days," says John Mora, author of Triathlon 101, "I think there was this perception that it was only for hard-body athletes, that it was a drill-sergeant type of activity. When people thought of triathlons, they thought of the Ironman"—the grueling Ur-race that involves 2.4 miles of swimming, 112 miles of cycling, and a full 26.2-mile marathon, in that order. Today, he points out, "the majority of participants in the large-scale events are just kind of average." Among the official rules for the Chicago triathlon, the nation's largest: "You may stop and rest during the swim . . . You may hang on to the guard boats or buoys." Curiously, in light of the sport's ripped-guy rep, how you placed matters little—it's cachet achieved by mere completion.

The mystique is what drew 30-year-old Pittsburgh native Jeremy Cornman to the sport 10 years ago. "At the beginning, I would say, maybe I liked the idea of being a triathlete more than actually being one," he says. Then, five years ago, he got involved with a woman who challenged both him and his ego, eventually turning him into a frequent Ironman competitor. Now he admits to scoffing a bit at the "one-and-done kind of guy—the corporate bigwig who tries to talk the talk, and has all the high-end gear, but has no idea what he's doing."