"How do we know what's manly? We really don't," he said. "There is no editorial guideline, so people interpret it their own way."

Each site embraces "manliness" in a different way.

Dartitup prides itself as "a guy's night out" and pairs you up with similar users during registration. It also has a "Challenges" section where users are asked to dart images in response to a challenge like finding "something Chuck Norris cannot defeat."

Manteresting gives you the option to "bump" or "shame" an image to the "Top Voted" or "Wall of Shame" sections of the site. Gentlemint has "Collections" that allow users to group images in whatever form they like as opposed to categorizing them.

AskMen's Poupada believes men share content differently than women and are more likely to share that which is representative of stereotypical male interests.

"It's more about what your stuff says about you," he said. "The sharing is very much in line with what society dictates to us. If a guy talks about calorie counting, he will be ostracized."

Poupada warns that the content on these niche websites could perpetuate stereotypes about what men are interested in. He's not alone. Gawker's Adrian Chen also mocked the idea of "Pinterest for men" in a recent article and suggested men are threatened by the female-dominated website.

"Why do we need these sad virtual man caves?" he wrote. "Get over yourselves, dudes. Maybe you'll even learn a little about closet organizing."

Manteresting's Patchin says his team has been accused of being "homophobic or misogynistic or sexist." But he points out that Manteresting has no restrictions against women joining, and that his site's 45,000 images of bacon doughnuts, basement game rooms and movie posters offer proof that there is a market for such content.

Harris of Dartitup says his site has received invite requests from women and that they are more than welcome to join.

"But we said from the start, this is a service that guys will like," he said.

More men on Pinterest

This raises a question: Would it be so terrible if Pinterest remains dominated by women and female-oriented content?

Mary Elizabeth Williams, a staff writer at Salon.com, wrote in a recent article that Pinterest's gender gap reveals how "conservative ideas about gender find themselves reproduced online."

But she believes that may not be such a bad thing.

"Within a seemingly tame array of cute animals and wedding ideas, nearly 20 years into Web culture, we have nevertheless somehow managed to create something formidable -- at long last, the Net's first true woman-centric blockbuster," she wrote.

Last week, Alexandra Lange wrote on The New Yorker's culture blog that she fears Pinterest's founders might "push the flowers off screen" because "women's interests are coming on 'a little strong' for an Important Social-Media Platform," she said.

She later added, "We should be long past women's clubs, but if Pinterest remains one, let it be the men's loss."

The scales of gender balance might already be leveling.

A recent Mashable slide show featured men with hundreds of thousands of followers on Pinterest. And according to Visual.ly, a data visualization community, 56 percent of Pinterest users in the UK are men.