It was last Friday, a few raw days after the presidential election. Adam Lee Jacobson was driving through Anchorage's University Medical District when he passed a man holding a cardboard sign that shocked him.

"Deport All Mexicans!" it said in bold letters. "Do What Donald Trump Want Mexicans take our Jobs"

"I couldn't really fathom how someone could feel that way, let alone how they could broadcast it like that," said Jacobson, a 34-year-old who works at two restaurants while studying business management at the University of Alaska Anchorage.

Jacobson made a split-second decision to pull over and talk to a stranger.

He didn't realize that what would happen next would be seen by millions of people around the world, or that the man had a back story few knew about.

Jacobson wanted to stand up to what he saw as prejudice in plain sight. So he parked his car and approached the man, standing on the sidewalk near the Providence hospital emergency room.

He pulled out his phone and started recording the conversation — in case things went sideways, and also to recount later.

The man holding the sign had an easy smile. He said he believed he'd been fired from Dairy Queen and replaced by people from Mexico who were paid less than minimum wage.

Jacobson argued back. The conversation lasted for two minutes.

Jacobson walked away feeling surprised: He had expected the man to be angry. His logic seemed way off but he had been pleasant, almost friendly.

Then he posted the video to his Facebook page so his 600 or so friends and followers could see it. One shared it. Then another.

He woke up Saturday and noticed the video was spreading. It had been viewed 4,000 times.

"That seemed like a huge, astonishing number to me," Jacobson said. It was nothing compared to what was to come.

Over the weekend, the video of the encounter on the Anchorage sidewalk was shared more than 25,000 times. By Monday morning it had 2.5 million views.

The scene joined a growing number of racially or ethnically charged incidents captured on phones and circulated on social media that have garnered intense attention in the days since the election.

It struck a nerve.

Late Sunday and early Monday, comments on the video were rolling in at 40 or 50 per minute; people from all over the world, many writing in Spanish, were reacting with outrage, anger and mockery.

In the more than 7,500 comments, people tore apart the man in the video, mocking not only his words but the cadence of his speech, the hat on his head, everything about him. Some threatened him with bodily harm.

But who was this man who was suddenly the target of so much national — even global — frustration and rage?

He was Matthew Brown, age 22. Unemployed but looking for a job. Diagnosed, Brown himself said, with "mild mental retardation."

On Friday, he said, he was hanging out on East Tudor Road when he got into a confrontation with a person he believed was Mexican outside a Taco King restaurant. In his anger, he walked to a nearby pizza shop and asked for some cardboard.

Brown's mother, Cynthia Olson, said she worries about him doing things like this. He doesn't think about consequences, about ways he might get himself hurt, she said.

When people meet her son, they often don't realize that he is mentally disabled, Olson said.

"He's been that way since he was young. He had a bicycle accident and a head injury," she said.

His court records show that he has been through Anchorage's mental health court, which tries to help people with mental illness or disabilities solve their problems while they resolve their legal issues. He's currently facing charges for allegedly stealing a car.

"The defendant apologized (to the owner of the car) and said he wanted to drive it around and show off to his friends," says a charging document in the case.

His mother said she has tried to get him into assisted living but he just leaves. She worries about him.

"I still love him," she said. "No matter what happens or anybody says about him, he's my son. I try and try."

Brown himself was worried by his sudden notoriety. Some people had figured out his identity online and sent him frightening messages.

"A couple of them are like, 'I'm going to kill you, I'm going to find you in a dark alley,'" he said.

"I want people to like me," he said. "I don't want them to hate me."

People on the internet knew none of this.

Jacobson didn't know either, until Monday morning, when the video was heading toward 2.5 million views and a reporter called him.

He said he was inspired to record the confrontation, in part, by his own history.

Two years ago, he and his husband awoke to find their U-Med area yard strewn with trash, and cards scrawled with things like "homos are possessed by demons" and "you're going to hell," tucked under their windshield wipers.

They filed a police report but never found out who did it.

The experience "reinforced my belief that sometimes you have to speak up and staying silent is contributing to the problem," Jacobson said.

He said some good had come out of the video: He'd gotten messages from more than 100 people thanking him for standing up against bigotry. He hadn't known Brown's back story. If he had known, he might have done things differently. He was disturbed to hear about the death threats. He was worried for him.

"I hope that his family and the people who are in his life will help him and work with him," Jacobson said.

After he got off the phone he began to reflect on how quickly an act meant to stand up to bigotry led to threats of violence by a faceless online mob.

Jacobson went back to Facebook and wrote a new post. Threatening people with violence is never OK, he said.

"He has every right to be dead-wrong in his beliefs, to broadcast those beliefs publicly, and to do so without fear for his safety," he wrote.

Jacobson decided he had to take the video down.

On Monday night, Brown could be found on the corner of Northern Lights Boulevard and A Street, holding another cardboard sign in the icy rush hour traffic. The only way he could make the problem go away was to apologize, he decided.

"Open boarder," this sign said. "Welcome Mexicans"