Since time immemorial, pot smoking has been a communal activity. Sitting on the grass, Bogarting a joint, being an herb hog — those behaviors were all frowned upon.

But today, when picking up germs from the tip of a joint or vape pen can leave you infected with the coronavirus, health-conscious potheads find themselves rethinking weed etiquette.

On a recent night downtown, Melissa Vitale, an avid and highly functional stoner, tokes away at one of the dozen joints she carries inside a silver cigarette case.

“We’re all making adjustments,” the 27-year-old publicist from Brooklyn tells The Post.

For instance, she advises putting the more vulnerable first: “People with compromised immune systems or without insurance will take the initial hit [of weed] before sharing with others,” she says.

In fact, Vitale, who works with the cannabis-positive clubhouse NSFW, has thought it through beyond that. “These days,” she says, “I’ll light a joint, take four to 10 hits and pass it. Then I light my own joint, which I hang onto. That way I am not getting anyone’s germs.”

It’s almost like she’s paying a kind of pothead health tax: For every five joints she lights, she gives away one-and-a-half in order to avoid the contagion. As for puffing joints that have been lit by others and passed to her, Vitale carries around a gold joint-tip. “It’s like a small cigarette holder,” she says. “I can insert the joint into it and have a clean tip.”

That might be a smart move all around. A new study indicates that while the coronavirus is typically transmitted through respiratory droplets, it can also remain suspended in the air for up to three hours, and on surfaces for up to three days.

In 2017, Philip Tierno, a professor of microbiology at NYU Grossman School of Medicine, told Vice that about 80 percent of all infectious disease is transmitted through direct and indirect contact — sharing a joint is considered direct contact. And don’t go thinking that lighter will kill off the germs either, he warns.

“The flame of the lighter at the tip of the joint will kill anything in the inferno,” he told Vice, “but not at the other end [of the joint] that goes in mouth — it’s still wet.”

To his chagrin, Matthew Janz can relate. This past Sunday, the 29-year-old director of THC marketing for the Source Dispensaries in Las Vegas went on a camping trip with a group of cannabis inclined friends — and they reconsidered their standard behavior.

“There is concern about puff, puff, passing,” he admits. “We only smoked from personal bowls.”

To make sure that the bongs were clean and that no germs remained from one person to the next, all bowls and bongs were scoured down with wipes containing 91 percent isopropyl rubbing alcohol. “It is the only substance strong enough to break down resins,” Janz says.

“And we decided to forgo joints.”

Nevertheless, Janz adds, sales of marijuana in the so-called flower form have risen at the Source, perhaps from those confronted with endless idle hours in self-isolation.

Janz and Vitale think of measures like these as their very own ways of social distancing in the middle of the public health emergency — without having to put aside their chill lifestyles.

To counter other potentially perilous situations with her favorite herb, Vitale keeps an assortment of single-use cannabis products on hand. They include edibles, tinctures and condiments.

However, she adds, “There is no way to sanitize the weed itself. So if that is how I get corona, from smoking weed, that is how I get it.”

Despite the inevitable constraints being brought on by the coronavirus, Vitale is doing her best to not let the virus harsh her mellow.

“I am using coronavirus as an excuse to wear silk scarves and driving gloves and to share less of my weed with people,” Vitale says, letting loose her trademark explosive laugh. “I am watching the world burn and lighting my weed in the fire.”