Comet Ping Pong customers came out to support the restaurant after a gunman entered it with an assault rifle, firing it at least once. Several other businesses on the block have received other threats as well. (Whitney Shefte/The Washington Post)

The fake news stuff we’ve been talking about?

That all just got real.

An entire D.C. neighborhood was on lockdown Sunday because some dope with a gun believed a fake news story that wildly and wrongly linked a neighborhood pizzeria to a child sex ring.

You could conclude that Edgar Maddison Welch, the ­28-year-old man from North Carolina who allegedly walked into the Comet Ping Pong restaurant carrying an assault rifle, pointed it at an employee and then fired one or more shots, may be a singular nut job.

The exterior of Comet Ping Pong, where a gunman showed up to “self-investigate” a fake story about a child sex ring. (Deb Lindsey /For The Washington Post)

He told police that he had come to the restaurant to “self-investigate” a false ­election-related conspiracy theory that linked Hillary Clinton to the child sex ring.

But he wasn’t the only dope who was roped into this.

A week before the presidential election, the son of retired Lt. Gen. Michael Flynn — the man President-elect Donald Trump has chosen as his national security adviser — shared the Comet Ping Pong conspiracy story.

Thousands of others shared it, too.

Days later, the retired general himself tweeted a hashtag referring to another fake news story that accused Clinton’s campaign chairman, John Podesta, of satanic rituals using bodily fluids.

That there, the satanic ritual stuff, is straight out of the grocery checkout line.

Remember when Americans used to laugh at the crazy-bad supermarket tabloid stories about “Bat Boy!” or “Titanic Survivors Alive!” or “Alien Bible Found! They worship Oprah!”?

D.C. police detained a gunman on Dec. 4, who had walked into Comet Ping Pong, a popular Northwest Washington restaurant and music venue. Police said no injuries were reported. (Faiz Siddiqui,Bastien Inzaurralde/The Washington Post)

What was different back then?

Why didn’t a desperado come storming toward the White House gates with his gun after the story about George W. Bush meeting with aliens hit the stands?

Because most people knew the source of the news — the National Enquirer, News of the World, etc. — wasn’t remotely serious, as lacking in nutrition as the candy bars the tabloids were displayed alongside.

But in today’s social-media universe, there’s a flood of stories from fake news sites that look legit. And stories that sound as ludicrous as alien love triangles don’t get a laugh; they get shared by our leaders, generating violent threats, dangerous reactions and, in the worst cases, bloodshed.

In an era when we have more access to more information than ever before, we’ve also become more willing to believe the crazy — and share it with others.

What happened at Comet Ping Pong isn’t the first time we’ve seen real consequences of the doctored-news phenomenon.

A year ago, a “gotcha” video — created by folks who lied, schemed and plotted to get a doctor to talk about the graphic details of her work while secretly being recorded — was pinging in the head of Robert Lewis Dear Jr. when he stormed a Planned Parenthood clinic in Colorado.

Dear used the phrase “no more baby parts” after he allegedly killed three people — a police officer, an Iraq War veteran and a mother of two — and injured nine others in that shooting rampage.

Grandstanding congressmen fed him the “baby parts” line after they watched that heavily edited video of a Planned Parenthood executive talking about the donation of tissue from aborted fetuses. (They must’ve forgotten that fetal tissue has been used in important medical research since the 1930s and helped produce vaccines for polio, measles and mumps.)

The video was created under false pretenses and never would have met the standards of a legitimate news organization.

That faux investigation ended in hours of congressional hearings, a budget crisis for Planned Parenthood in many states and the deaths of those three people in Colorado.

Five years ago, it wasn’t fake news but an equally careless use of words that helped incite an equally terrible burst of violence.

Supporters of former Alaska governor Sarah Palin put out a map with crosshairs targeting the districts of 20 House Democrats and urging folks: “Don’t Retreat, Instead — RELOAD!”

Then-Rep. Gabrielle Giffords (D-Ariz.) was on that map and criticized it as soon as it was posted online and her office was vandalized.

“We’re on Sarah Palin’s targeted list, but the thing is that the way she has it depicted has the crosshairs of a gun sight over our district,” Giffords told MSNBC at the time. “When people do that, they’ve got to realize there’s consequences to that action.”

On Jan. 8, 2011, the consequences were chilling: Jared Loughner showed up with a gun outside a Tucson supermarket where Giffords was greeting constituents and killed six people and injured 20 more, including Giffords.

Still, as the funerals were being held and Giffords was in intensive care, Palin’s supporters insisted that crosshairs were never a reference to guns.

Words matter.

That kind of disregard for common sense and responsibility has kudzued into what we have today — educated leaders willing to believe conspiracy theories about child sex rings and satanic rituals thanks to nothing more than a slick-looking online story.

Get a grip, America.

The owner of Comet Ping Pong had endured weeks of death threats. Phone calls, messages, stalkers, employees being harassed.

They’ve all complained about the relentless attacks. Then they faced a real attack, which has left a business and a neighborhood deeply shaken.

“Let me state unequivocally: these stories are completely and entirely false, and there is no basis in fact to any of them,” owner James Alefantis wrote on his Comet Ping Pong Facebook page Sunday night.

There is no FBI investigation, no New York Police Department takedown. None of that.

“What happened today demonstrates that promoting false and reckless conspiracy theories comes with consequences,” Alefantis wrote. “I hope that those involved in fanning these flames will take a moment to contemplate what happened here today, and stop promoting these falsehoods right away.”

Those who run our social-media companies and Internet search engines need to find a way to help a gullible country differentiate between fake news and real news. Let’s make America believe in facts again.

Twitter: @petulad