A man opened a can of tuna on a flight. The internet gasped.

Ally Jaksen was trying to sleep on a morning flight from Anchorage to Seattle last month when her seat neighbor busted out a controversial breakfast: a can of tuna. He ate it with a fork. He made little cracker sandwiches with it.

“It felt too odd and crazy to even be real,” said Jaksen, 26, who travels two or three times a month. “I’ve literally never seen anything like this.”

A content creator, Jaksen turned her experience into a TikTok that has gotten more than 1.8 million views - and plenty of opinions. She made her own thoughts clear in the video, writing: “Canned tuna on the plane gotta be up there in terms of crimes against humanity.”

A search of social media shows that Jaksen has company: Many travelers have posted their horror about a seatmate’s tuna meal. Some have bashfully admitted to being the fish-consuming passengers themselves. One woman posted a video of herself eating a tuna sub from what appeared to be the lavatory on her plane with the explanation: “It was starting to smell, you guys. I’m in the middle seat.”

In the volumes of writing that have been dedicated to flying etiquette, the verdict is clear: Eating pungent, messy food - with tuna sandwiches a prime example - is usually considered a faux pas. (As The Washington Post wrote last year: “If your cat likes it, consider it a no.”)

National etiquette expert Diane Gottsman, owner of the Protocol School of Texas, said that because there are no official rules against bringing odoriferous foods on a plane, “it’s really up to us as courteous passengers to make good decisions.”

Foods like tuna and egg salad generally have a strong smell and should be finished before boarding a plane, she said. After hearing details of Jaksen’s flight, Gottsman declared the practice of eating tuna directly from the can or assembling mini sandwiches “so disrespectful on so many different levels,” because the diner is turning the plane into his kitchen.

“So bad. That is a no,” she said. “That’s going to protocol prison.”

Passengers seated near someone consuming those foods could ask a flight attendant about switching seats. Confronting the passenger who is chowing down could be tricky and lead to an uncomfortable flight, Gottsman said.

“It should not be up to fellow passengers to ask you to put your food away,” she wrote in an email, before digging into the issue on a phone call. “It might start an onboard argument, and that’s why it’s best to ask assistance from the flight attendant if the smell is really bothersome or you are allergic.”

Flight attendants - or at least two specific ones who happen to be married to each other - are divided on the topic.

Rich Henderson, who runs the Two Guys on a Plane blog and social media accounts with his husband, Andrew, said in a message that he believes heavily scented foods, colognes and other odors do not belong on planes.

“Anything that would smell strongly in a confined shared space and could potentially disturb other passengers is a no in my book!” he wrote.

His husband, Andrew Henderson, had a different take. He loves to bring tuna to work as an easy meal.

“Honestly there are so many offensive smells on an airplane sometimes, so if it’s not tuna fish then it’s probably someone with their shoes off or some other smell,” he said in a message.

Jaksen, who gained a TikTok following with cooking videos from her “kathroom,” or kitchen-bathroom area in New York City, said she actually likes tuna. And she is not without sin: She recalls the time she and her boyfriend brought hot wings from John F. Kennedy International Airport’s Buffalo Wild Wings on a flight, after they ran out of time to eat them before boarding.

“That is a one-time occurrence and will never happen again,” said Jaksen, who lives in Denver. She did not show the tuna-and-crackers man’s identity and said he did not ask whether it was okay to eat the food, which she described as “a little smelly.”

Comments on her video came out largely opposed to the man’s snack choice; several people shared their own stories of fellow passengers eating hard-boiled eggs, dried sardines, Slim Jims or fried fish.

Some, however, praised tuna as a quality protein choice. At least one pointed out that the can appeared to be a premade Bumble Bee tuna salad with a less-offensive smell than regular fish. (A home test of the brand’s tuna salad revealed an odor.)

“I think overwhelmingly it was more so like, ‘Oh my God, get him on the no-fly list,’” Jaksen said. “Obviously, that’s a joke.”