In the latest branding blunder making America wonder why this idea wasn’t erased from the whiteboard after the first brainstorming session, Coca-Cola and Delta Airlines collaborated on “creepy” in-flight napkins that have been lambasted on social media as a naughty invitation for a booty call and worse.

The napkins are an unusually cheeky step out of both Coke and Delta’s comfort zones, raising questions about how companies so concerned about the minutiae of their brands could have missed such critical social clues, said luxury branding expert Ali Craig, who helps her clients connect emotionally with their customers in their marketing materials.

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One flirty napkin message said: “Be a little old school. Write down your number and give it to your plane crush. You never know …”

Indeed, “you never know” at all.

A fellow passenger’s intent might be to sexually assault or stalk you until you have to go underground in witness protection — or so goes the social media blowback calling the marketing campaign culturally tone deaf and downright weird.

One of the reasons the napkin debacle is so stunningly awkward for Delta is that its name came up “a fair number of times” in a wave of reports that caused the FBI to warn of an “alarming” increase in sexual assaults on airplanes, Craig said. Its image already badly bruised over technology issues that grounded thousands of flights last year and a string of in-flight pet deaths, this incident only made matters worse for the beleagured airline.

“If it was JetBlue or Virgin, you might expect a little twerking outside the box,” Craig said. “But for that to have left Coke and gone over to Delta, a very conservative brand trying to stay out of trouble — even the flight attendants didn’t get a look at it. If they had, they might have said, ‘Hey, HR, this may be an issue.’ “

Craig said it’s equally baffling that it never occurred to “straight-laced Coke, the company of Santa Claus and and that good, old American thing, that someone might say ‘Hey, you crossed the line there.’

“They spend millions protecting their brand and do a magnificent job keeping their brand message on track,” she said. “For this goof to happen, someone just didn’t think it all the way through.”

Craig thinks Delta was probably trying to capture some of the same magic that has come Southwest Airlines’ way with a campaign that uses emotional storytelling to connect with customers on its interactive microsite, 175 Stories. The premise is that every seat has a story, whether it was once occupied by a little girl who flies frequently to and from a hospital in St. Louis because she got a lung transplant as a baby or strangers who found themselves seated together, fell in love and got married.

But the campaign splattered like it had been dropped from a jetliner cruising at 39,000 feet.

Both companies issued apologies, saying they had been working to eliminate the napkins for weeks, long before the widespread social media smackdown on the messaging.

“We rotate Coke products regularly as part of our brand partnership, but missed the mark with this one,” Delta said in a statement. “We are sorry for that and began removing the napkins from our aircraft in January.”

Coca-Cola said in its statement: “We sincerely apologize to anyone we may have offended. We worked with our partners at Delta to begin removing the napkins last month and are replacing them with other designs.”

Too often, companies try too hard to be humorous and clever, worrying “if I don’t do something fun, my customers will think I’m boring,” Craig said. “It may be smarter to be a little less playful than to open wounds the brand had no intention of opening.

“Society is so hypersensitive to so many things — others’ opinions, our own opinions — that sometimes people look for things to take offense about,” she said. “This is going to get worse and worse.”

Delta and Coca-Cola have moved on from the controversy in their social media strategy.

“Coke has been trying to do some PR-fixing, but I’m willing to bet both are waiting for it to pass — and it will, as long as someone doesn’t come out and say, ‘the napkin made me do it.’ “

Photo: Mario Tama/Getty Images