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.”