When David Dulin celebrated his 36th birthday in March, he asked his Twitter followers for just two things: cash donations to his online payment account, and pictures of them in their own birthday suits.

“It started as a joke, but it’s just become something that we run with,” said Mr. Dulin, a retail worker in Charlotte, N.C. “Almost every birthday I’ll be like, ‘OK, Cash App and nudes: Drop them!’”

Mr. Dulin began coyly asking for nude photographs via social media on his birthday a few years ago as something of a test after seeing other gay men make similar requests on their own birthdays. He was surprised, he said, when some of his online acquaintances delivered on the invitation, admitting that they had been looking for an opportunity to flirt with him.

In recent years, many queer men have begun sending and receiving nude selfies on social media for their birthdays. Variations on “It’s my birthday, send nudes” have been uttered so frequently online that it has become something of a meme (or, at the very least, a generic way for a gay man to announce his birthday, whether or not he actually expects to receive any explicit images). The practice has become so normalized that the request is sometimes simplified to, “It’s my birthday — you know what to do.”

Brendan Drake, 36, a choreographer in Los Angeles who identifies as genderqueer, said he had made the request so often that this year on his birthday he received nudes from friends without even having to ask. “It’s almost like it was expected,” he said.

The trend of gay men soliciting nudes on their birthday speaks to the unique nature of gay friendships, but also plays into a social media culture that rewards humor, according to Tom Roach, who teaches gender and sexuality studies at Bryant University in Smithfield, R.I.

“I think it’s basically a provocation and a challenge, but in a campy way — it has a certain ‘wink, wink, nod, nod’ feel to it,” said Professor Roach, who has written books on queer friendships and digital relationships. “I don’t think people are sincerely, desperately seeking nude pictures of their friends. I think they’re doing it to be provocative, to be like, ‘Look at how shamelessly sex-positive I am!’”

In many parts of the country, it is not uncommon for gay people to have a more relaxed attitude toward sex, including alternatives to monogamy such as open relationships, and many gay friendships begin as casual sex encounters. A 2022 study also found that 85 percent of respondents who were in same-sex relationships had formed romantic partnerships out of friendships, while only 68 percent of all respondents said they had taken the “friends-to-lovers pathway.”

Gay men, of course, are not a monolith. But given the community was born out of a shared sexual attraction to men, Professor Roach said, it doesn’t surprise him that friendships between gay men today “don’t play by the same rules” as others.

In addition to cellphone cameras making it far easier to quickly snap and send a racy photo, social media apps like Instagram and X — the platform formerly known as Twitter — allow users to curate private lists of “close friends.” For many gay men, the feature can be used to ensure that an open call for birthday nudes reaches only a carefully selected audience — one excluding straight friends and colleagues.

Some of these behaviors mimic well-established practices on hookup apps, where the trading of sexually explicit images can be de rigueur. “It’s also importing some of the norms of Grindr into other platforms that don’t necessarily traffic in nudes,” Professor Roach said. “It’s kind of like worlds colliding.”

A birthday can also pose an opportunity for someone ordinarily too shy to solicit nudes to do so in a socially sanctioned way, while the messages themselves can function as an all-purpose declaration of consent for others to shoot their shot in the most risqué way possible.

“It really feels like a way of publicly doing so where the shame will just be slightly less,” said Manuel Betancourt, 38, the author of “The Male Gazed,” a collection of essays on thirst traps and queer longing. “Then, it can be a door, or it can be a window, or it could be sort of an opening into something else.”

The decision to send a birthday nude is often predicated on feelings of attraction, but it’s not always about seeking sex. Jake Niemeyer, a 32-year-old television editor in Los Angeles, said he had sent birthday nudes to online acquaintances as far away as Scotland with no expectations of physical intimacy.

“There’s next to no chance I will ever see this person in-person,” Mr. Niemeyer said. “But still, I find them attractive, they say they find me attractive and that’s kind of a nice feeling. It’s a safe way for both of you to have a micro sexual interaction.”

In a group that often celebrates and rewards idealized muscular bodies, leading some gay men to develop body-image issues, the act of swapping nudes with trusted friends can actually prove to be deeply affirming.

“It’s very body-positive,” said Zachary Zane, 32, a bisexual sex columnist. “You feel sexy, you feel affirmed, you feel validated and loved by your friends. It’s not an invitation to hook up; it’s more so us actually just supporting each other and showing each other love.”

The pandemic isolation of 2020 may have fueled the sharing of nude images among gay men who felt cut off from one another. For Mr. Drake, the choreographer, those fearful months made him worry less about whether his nude images were floating around online. Alone for several months with just his phone for company, he also found important intimacy in trading nudes with friends.

Having an online outlet for sexual expression “was actually a little lifesaving for me,” Mr. Drake said. “A lot of people will call it toxic, but I don’t think it’s toxic. I think it’s really life-affirming.”