“Everyone has a body,” the man says.

He’s standing on the concrete at World War I Memorial Park in Lawrenceville, holding his bicycle upright. On a night like this, and in this particular park, his words could take on a political charge—it’s late July, and President Trump’s ban on transgender people serving in the military has dominated the headlines.

But the weight of the man’s words is undercut, at least momentarily, by one glaring fact: He’s standing here in his boxers.

And so am I.

Welcome to the Pittsburgh Underwear Bike Ride: a gathering that, once a month from May to October, brings out hundreds of half-clad Pittsburghers for a three-hour ride in support of body positivity. It’s 8 p.m. and already it’s a been a night of several firsts for me: leaving my house unclothed, riding down Butler Street in boxers, and now, conducting my naked-est interview to date.

The man is Paul Beaver, a regular at these rides and—like everyone else I’ll meet tonight—a sort of Underwear Bike Ride evangelist. “The point is to show up and have fun in whatever you’re comfortable in. If you’re not comfortable rocking some tighty-whities or a thong, wear shorts. Wear a t-shirt. Wear a burqa. You’ll come to this ride and see everything from topless women in bikini shorts to guys wearing t-shirts and jeans. It’s all about whatever you’re comfortable presenting to the world.”

I look around. He’s right: There are maybe 75 cyclists milling about in various stages of undress, with more showing up by the minute. Some arrive topless and covered in glitter; others seem hesitant to take off their shirts. I see all ages, races and body types. A hard-of-hearing older man wanders around in his briefs, offering hugs to strangers.

Maybe there’s safety in numbers, I suggest to the woman next to me. She introduces herself as Payden Vietmeier, a yoga teacher who’s been coming to the ride for years. “It’s just so much fun,” she says as she takes off her shirt. “You get to be with a bunch of weirdos, and you get to feel normal for once.”

I ask whether she has advice for first-timers. “Don’t be afraid of your farmer’s tan,” she says. “Everybody has their weird tan lines going on. You’ll be one in a hundred. I promise!”

At the heart of it all is Scott Kowalski, a local cycling advocate, and—as of last year—the Underwear Bike Ride’s lead organizer. Launched in 2012 by Kowalski’s friend, Virginia McGrath, the ride has grown from 20-30 riders in its first year to anywhere from 200-300 today.

“Body positivity was always the idea behind it,” Kowalski says of the ride. “It’s an important issue, and it draws a great mix of people. The crowd has changed and flowed over the years, but I’m really proud of the fact that there are so many diverse groups here now. It shows you can be comfortable—and that if you’re not comfortable, you can come here and be comfortable.”

That ethos has popularized the ride in Pittsburgh and beyond. Though there’s no central governing body of underwear bike riders, similar events take place in Chicago, Dallas, Minneapolis and elsewhere. McGrath brought it to Pittsburgh from Milwaukee, Kowalski says; when she moved on, he “didn’t want to let it die.”

Kowalski leaps onto a park bench. The ride is about to begin.

Despite the event’s playful nature, Kowalski and his team of volunteers take safety seriously. Yes, we’re in our underwear and there are lots of us, Kowalski tells the crowd from atop the bench, but it’s also getting dark and there are still plenty of cars on the road. He rattles off the rules: No texting or picture taking while riding. No unpredictable stops or sudden slowdowns. Listen to the ride marshals, who’ll guide the crowd along a pre-planned route.

Then he gets to the most important rule, which the ride’s regulars shout in unison: “Don’t be a jagoff!”

With that, a deluge of near-naked bodies spills onto Butler Street . . .