Mankinis. Tuxedo-printed briefs. Men in red lingerie. A woman dressed only in flesh-colored underwear and two black “censored” signs.

As the founders and organizers of Cupid’s Undie Run, Bobby Gill, 28, and Brendan Hanrahan, 27, have seen it all — and they’re expecting the same creativity Saturday, as 800 runners strip down for a 1.5-mile jaunt on Capitol Hill.

“Anything goes,” Hanrahan says, “except thongs.”

“And pasties,” Gill adds quickly. “We had to make that rule when a group of older women contacted us about wearing them. Definitely no pasties.”

It may not sound like it, but Cupid’s Undie Run, now in its third year, is more than just an opportunity for D.C. area exhibitionists to drop trou.

The run was born in 2010 as Hanrahan, of Silver Spring, racked his brain for a way to raise money for the Children’s Tumor Foundation.

When Hanrahan was a teenager in Georgia, his best friend’s 10-year-old brother, Drew Leathers, developed what Hanrahan describes as “random tumors” on his arms, back, shoulder, thigh and other body parts.

“One tumor they removed from his calf was the size of a racquetball,” Hanrahan recalls.

Drew was diagnosed with a rare genetic disease called schwannomatosis, a form of neurofibromatosis, which causes noncancerous tumors to grow on the body’s nerves. Neurofibromatosis affects about 100,000 Americans, many of them children.

By the time Drew was 16, the growth of the tumors had progressed to the point where he was “bedridden and immobilized” by nerve pain, Hanrahan says.

There is no cure for the disease, and treatment involves surgically removing the tumors.

In Drew’s honor, his brothers, Chad and Ben, began an organization called the “Tumornators,” and Hanrahan helped them raise money for the Children’s Tumor Foundation.

“When I moved to Maryland [in 2006], I knew I wanted to do something similar in D.C. that wasn’t just another happy hour or 5K,” Hanrahan says.

Inspiration struck in early 2010. Hanrahan heard about a holiday-themed fundraising event in Boston in which people run in Speedos and Santa hats to benefit charities.

Hanrahan partnered with Gill, his housemate at the time, and the duo began floating the idea of a run with a Valentine’s Day theme. With about a month until the day of the run, they expected 30 or 40 people to sign up to strip down for the Children’s Tumor Foundation.

On race day, 650 people showed up.

“We looked at each other and said, ‘Good God, what have we done?’ ” says Gill, who now lives in Northwest Washington.

In its first year, Cupid’s Undie Run raised about $8,000 for the Children’s Tumor Foundation based solely on registration fees. In 2011, Hanrahan and Gill implemented an option for runners to do additional fundraising; more than $52,000 was donated to the foundation.

This year, Hanrahan and Gill expanded the event, adding run locations in Denver, Cincinnati, Atlanta, Seattle and New York, where their friend Chad Leathers, Drew’s brother, is organizing the event. Registration for the District run sold out in December.

Two weeks before the run, fundraising had broken the $100,000 mark, and even in the final days, donations are continuing to roll in.

One thing that has struck Hanrahan and Gill is the support they’ve received from people who aren’t personally affected by the disease.

“There’s no one in my family with neurofibromatosis,” Gill says. “No one in Brendan’s family. Some of our top fundraisers aren’t related to anyone with it. But as the word gets out, people realize it’s such a tragedy to see this happen to a child.”

Some runners have gotten creative with their fundraising efforts. One, Antwone Walters, auctioned off his “indentured-labor-ness” through Facebook posts, offering to do odd jobs in exchange for donations.

“You must be local,” Walters noted in his post. “I’m not traveling to GA to take [your] dog for a walk.”

Zach Bender, a runner with an especially hairy body, is auctioning “chest space.” His largest donor can choose a PG-rated, Valentine’s-related shape for him to shave into his chest hair.

“We love that kind of enthusiasm,” Gill says.

Hanrahan and Gill are grateful for the support from runners and donors, but they don’t fail to recognize the event’s MVP.

“The run would be nothing without the underwear,” Hanrahan says. “The appeal is the underwear.”

For those who are nervous about “stripping down to their skivvies,” Gill says, the run is bookended by parties at Capitol Lounge and the Pour House on Pennsylvania Avenue SE.

“A little bit of liquid courage,” he says with a wink. “And just think: This is the one opportunity to run around the Capitol in your underwear without getting arrested.”