It all started when a “self-taught engineer, extreme introvert, science-nerd, anime-lover, college dropout” wrote that she was tired of stereotypes.

Isis Wenger, a 22-year-old platform engineer in San Francisco, got talked into being one of a handful of colleagues featured in a hastily organized recruiting campaign for her company OneLogin, she wrote on Medium.

The response shocked her. Friends forwarded her posts from complete strangers responding to the photo, and soon they didn’t need to send them — they were everywhere.

“… if you knew me you would probably know that being famous is one of my biggest nightmares; seriously right up there with falling into a porta potty,” she wrote.

Still, there was her image, triggering all this reaction — a lot of it negative. And a lot of it mirroring attitudes she often saw in the tech world, she wrote — from men who seemed like pretty smart and normal guys who didn’t know how uncomfortable their comments might make someone.

Like when male colleagues threw dollar bills at her in the office.

She ended the post with  a challenge:

“Do you feel passionately about helping spread awareness about tech gender diversity?

“Do you not fit the ‘cookie-cutter mold’ of what people believe engineers ‘should look like?’

“If you answered yes to any of these questions, I invite you to help spread the word and help us redefine ‘what an engineer should look like’ #iLookLikeAnEngineer.”

And she posted a photo of herself with the hashtag.

It took off.

“I think the message went viral because it’s not just my message,” Wenger wrote in response to questions from The Post. That’s why she made sure the hashtag was so all-encompassing. “It addresses a problem that many people of different genders and ethnic backgrounds face.”

“Especially when I was first starting out in the industry, people were very condescending,” she said. “There’s no way I could have really been an engineer right? They had pretty low expectations of me.”

But growing up, the only child of a single mother, a teacher, she had already taught herself to build Web sites by the time she was 8, by right-clicking ” ‘view source’ on Neopets and reverse-engineering bits of code to figure out what each individual tag did.”

If colleagues had low expectations, she quickly showed them up.

Soon there were #Ilooklikeanengineer tweets from women all over the world (and a few men) (and other creatures), tired of surprised looks when they meet a client for the first time, or arrive at an interview.

By early Tuesday afternoon San Francisco time, the hashtag had sparked 36,000 tweets, and other innovations, like this page — showing women in caps and gowns, Lilly Pulitzer and pink hair — a storytelling app about diversity in tech, and a T-shirt someone designed featuring the hashtag with half the proceeds going to a charity Wenger selects. “Honestly, I consider it all to be very heartwarming and inspiring,” she wrote.

When she was in college at West Virginia University, Emily Calandrelli, who posted a photo of herself with that hashtag at Lick Observatory in California, was one of just two women in a big science class. “We definitely stood out.”

And when she meets new people, if her graduate education in aeronautics and astronautics, technology and policy comes up, she often hears, “Wow, you don’t look like you went to MIT!”

“They say it’s like it’s a compliment,” she said, “but it rubs me the wrong way. Being interested in science and engineering is not a male quality. This movement proves that’s not the case.”

She was surprised that so many people posted photos but said it was fun scrolling through seeing the incredible diversity of images and felt that, once the idea picked up momentum, “you wanted to be part of that community.”

Now the host and producer of FOX’s “Xploration Outer Space,” Calandrelli interviews experts in space exploration about their research. “A lot of times when I walk into those environments they make the assumption that I don’t have an understanding of science of space exploration – perhaps because I’m a woman, or how I present myself on camera, with makeup, hair, all that.” So she could immediately relate to Wenger’s experience.

When Calandrelli asked an engineer at a company developing a spacecraft about the type of propulsion they were using and the specific challenges they were having in its design, “the guy looked at me and said, ‘Did one of my guys tell you to ask that?’ ”

There could have been a few reasons why he was surprised, she said; maybe it was a hurdle they were facing that very day and he didn’t expect such a topical question.

“In my head I was thinking, ‘If I were a big burly man, would you ask this?’

“ ‘Nope,’ she told him. ‘I came up with that question all by myself.’ ”

Here are just a few of the photos people were posting with the hashtag:

Like any great social media wave, it got kooky, too.

Small wonder Wenger is “experiencing a lot of cognitive dissonance.”

As a soft-spoken but strong-willed person, “It’s simultaneously overwhelming and incredibly empowering to feel like I am genuinely helping increase awareness.”