Joel Pavelski, 27, isn’t the first person who has lied to his boss to scam some time off work.

But inventing a friend’s funeral, when in fact he was building a treehouse — then blogging and tweeting about it to be sure everyone at the office noticed? That feels new.

Such was a recent management challenge at Mic, a five-year-old website in New York that is vying to become a leading news source created by and for millennials. Recent headlines include “Don’t Ban Muslims, Ban Hoverboards” and “When Men Draw Vaginas.”

“There’s 80 million millennials; we focus on the 40 that went to college,” said Chris Altchek, Mic’s 28-year-old chief executive.

But he is still working out how to manage many of the traits associated with his fellow millennials: a sense of entitlement, a tendency to overshare on social media, and frankness verging on insubordination.

Mic’s staff of 106 looks a lot like its target demographic: trim 20-somethings, with beards on the men and cute outfits on the women, who end every sentence with an exclamation point and use the word “literally” a lot.

Their crowded newsroom on Hudson Street has an aggressively playful vibe, like a middle-school fraternity house. Some ride hoverboards into the kitchen for the free snacks. Others wield Nerf dart guns or use a megaphone for ad hoc announcements. Dino, a white Maltese terrier owned by the lead designer, snuffles between desks.

Mr. Altchek is proud of the freewheeling office culture. “It helps us to have everyone speak out and best ideas rise to the top,” he said. “What that can feel like or sound like is rudeness. But I’d rather have a lot of people speaking their minds than a very controlled environment.”

But running an office made up exclusively of millennials, it turns out, is not without its snags. His philosophy was tested when Mr. Pavelski, Mic’s director of programming, requested a week off, ostensibly to attend a wake back home in Wisconsin. “I went to talk to Joel and said, ‘So sorry about your loss, take as much time as you need,’” Mr. Altchek said.

Then, several days later, he noticed Mr. Pavelski tweet a link to Medium, a popular blog for cathartic, personal essays. In a post titled, “How to Lose Your Mind and Build a Treehouse,” Mr. Pavelski wrote about feeling burned out at work and wanting to rebuild a childhood treehouse as therapy. The first line read, “I said that I was leaving town for a funeral, but I lied.”

“I was sort of taken aback,” Mr. Althchek said. “It’s not acceptable to be lied to.”

In a disciplinary meeting the next day, Mr. Pavelski’s supervisor acknowledged that he had been working grueling hours, so he was given another chance. Still, Mr. Altchek wanted to send a message. “Our feedback to him was, ‘This is not a three-strike policy, it’s a two-strike policy,’” he said.

Mr. Pavelski is still on his first strike. But even in an office that is tolerant of youthful boundary pushing, some millennial behavior can cross the line.

Mr. Altchek recalled a companywide meeting last September that coincided with the religious holidays Yom Kippur and Eid al-Adha. An Anglo-Pakistani employee asked why management had announced a flexible time off policy for the Jewish holiday, but not for its Muslim counterpart.

“So I told her, ‘Great point, being inclusive and respectful of all religious affiliations is incredibly important to Mic,’” Mr. Altchek said.

Afterward, in front of a smaller group, he was approached by a younger, entry-level employee who said that there were two words missing from his reply. “I was a bit confused and said, ‘O.K., what were those?’” he recalled. “And she said: ‘I’m sorry. I didn’t hear an apology.’”

Mr. Altchek did not think such a comment belonged in a workplace, especially his.

“I was a little taken aback by the tone, but I told her I would address it and make sure the person who asked the question wasn’t offended by the answer,” he said. “You have to control your temper. It was in front of a bunch of people, which was probably better, because I was forced to be calm.”

That employee is no longer with the company. (Mr. Altchek said she was let go for “performance-related issues.”)

A sense of entitlement is not the only stereotype attached to millennials in the workplace.

“Entitled, lazy, narcissistic and addicted to social media,” according to CNBC. “They Don’t Need Trophies but They Want Reinforcement,” Forbes wrote. “Many millennials want to make the world a better place, and the future of work lies in inspiring them,” Fast Company proclaimed.

Older managers confused by why millennials like to Snapchat with co-workers, or don’t want to pay their dues with grunt work, had better get used to it. Last year, millennials edged out Generation X (35 to 50 years old in 2015) as the largest share of the labor force, according to the Pew Research Center. What’s more, millennials have also surpassed baby boomers.

Joan Kuhl, 36, who founded Why Millennials Matter, a consulting firm that advises employers like Goldman Sachs on hiring and retaining recent college graduates, said that what is needed is more familiarity.

“We tend to publicize these outrageous acts of defiance, versus emphasizing the majority that I run into and work with, who are very mission focused and value based,” she said.

Ms. Kuhl educates her clients on the quirks of millennials, and why a 21-year-old sees nothing wrong with oversharing. Millennials are pushed to create a “strong personal brand” to land a job, Ms. Kuhl said, so asking them to tone it down once they are employed sends “a lot of mixed messages.”

Still, even Ms. Kuhl has been taken aback by some of the millennials in her office. She remembered an intern who ate a tuna fish sandwich during a 10 a.m. meeting with very senior colleagues. When mildly rebuked afterward, the intern replied, “Well, you said to be myself, and I was hungry.”

So imagine a workplace where all are in their 20s.

Mr. Altchek founded Mic in 2011 (then operating as PolicyMic) with Jake Horowitz, now 28, his former classmate from the Horace Mann School in New York.

Today, Mr. Horowitz reports from the field (such as the Syrian migrant crisis from the beaches of Greece, and interviewing President Obama in the White House), while Mr. Altchek runs the business out of a 15,000-square-foot converted warehouse in the Hudson Square neighborhood.

Millennial news has significant competition for eyeballs. According to the data provider comScore, Mic had about 19 million unique visitors in January, compared with 79.7 million for BuzzFeed, with five other competitors falling in between. (A Mic spokeswoman pointed out that rivals like Vice Media operate multiple branded sites that roll into their comScore number, whereas Mic relies on just one site.)

At Mic, part of the growth strategy is not just airing, but blaring, its business on social media.

Hence there are office conversations held on Twitter, and the blurring of personal and professional boundaries, such as when Mr. Altchek broadcast his dental examination on Periscope, a live streaming video app.

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Indeed, several Mic staffers cited the “say anything” office culture as one of the things they loved most about working there.

“People are here from morning to night, and we don’t want to leave,” said Elizabeth Plank, 28, a high-energy reporter who lives in the East Village and hosted a video series called “Flip the Script,” which seeks to challenge assumptions like, “What Happens When a Lady ‘Manspreads.’

Ms. Plank contrasted her freedoms at Mic to her previous job at a feminist nonprofit organization, which she regarded as exemplifying the outdated work practices of older people.

“We called people on phones and we — I don’t know — we faxed people,” Ms. Plank said, sounding exasperated. “And we had to mail things. And no one really took my opinion into consideration.”

At Mic, she was able to dabble in different jobs and negotiate grandiose titles like “executive social editor.” Often, she prefers the theater of tweeting back and forth with the editor she sits next to rather than speaking face to face.

“If you can be young at heart, I think it makes your personal, and not only your work life, better,” added Ms. Plank, who left for Vox last month after two and a half years at Mic.

Perhaps because of this very culture of workplace-as-reality-show, Mr. Pavelski, the prevaricating treehouse builder, remains notably unchastened.

“Maybe this is because I’m young, but, like, I don’t think that there is a lot about my personal life that I wouldn’t want to incorporate into what I’m doing professionally,” he said. “The reason I wrote that essay in the first place was about catharsis, and I wanted to walk through my thought process and figure out what was going on with me.”

The logic of that may be more apparent to his age group.

“The one thing I don’t want people to mistake is that we’re serious about this,” he added. “And that we’re taking over. That is all.”