On a scorching June day on the Amalfi Coast of Italy, Chloe Madison and her boyfriend, Colin Pinello, stopped to have lunch in Positano, a glamorous town overlooking the Mediterranean Sea.

With their refreshing caprese pasta plates and Aperol spritzes, they had one thought on their minds: ice water. But they knew that asking for it would be too American. While the Europeans around them seemed unfazed by the temperatures, she said, they felt parched.

“Water was something we consistently had to request,” she said, and when they asked for ice it was “just a few cubes.”

Ms. Madison, 27, decided to poke fun at this, posting a TikTok video of the couple fanning themselves with the caption: “fighting the American urge to ask for a cup of ice water in Europe.” (In this, she joined a trend of Americans wanting frosty drinks in tourist hot spots, with some musing on social media if Europeans simply don’t drink water).

With U.S. tourists returning in high numbers to Europe this summer and heat waves also setting records, American sensibilities about staying cool are butting up against European etiquette and norms. (Some tourists are changing their travel plans because of the heat.) Amid the broader climate change crisis, a penchant for flip-flops, shorts and guzzling ice water may seem trivial, but those differences can be stark.

Savvy travelers seeking to blend in with the locals have increasingly turned to social media, particularly TikTok, for advice and commiseration. Much of the guidance will sound familiar to seasoned travelers.

For example, be careful about small talk and asking personal questions of strangers. Don’t be surprised that many Europeans still smoke in cafes and other public places. Do a little research about local customs and learn some basic conversational phrases in the local language.

There’s also this standard advice for Americans: “Be less loud.”

But the record high temperatures in Europe have led to a new theme in online travel advice.

“I couldn’t help but notice the striking contrast between how Americans and Europeans handle a heat wave,” Ms. Madison observed, saying that Europeans “didn’t appear to rely as heavily on things Americans consider essential.”

The experts agree. For a start, don’t expect a big water pitcher filled with ice cubes the moment you sit down in a restaurant.

“It’s not common at all in Europe,” said Viviane Neri, director of the Institut Villa Pierrefeu, a finishing school in Montreux, Switzerland. “In some places, the restaurants have an obligation to serve tap water, but they charge for it nevertheless, because they say we have to wash the bottle and the glass and everything.”

Nor has the American cold brew fad permeated the continent. If you order iced coffee at a local shop, it’ll look more like a Greek frappé or a caffé freddo. In some places, it’s simply not an option unless there happens to be an American coffee chain.

“Iced coffee in America is a thing, and I’m going to be honest, I love it,” said Ilaria Rondinelli Huey, 30, an Italian TikTok creator who moved to the United States a few years ago. “That’s something that I miss when I am in Italy.”

Ms. Rondinelli Huey suggested having traditional hot coffee for breakfast and then ordering an Aperol spritz at lunch.

Also: “We don’t put ice in our wine.”

Travelers from the United States also shouldn’t expect air-conditioning or other power-hungry conveniences.

Europeans are more concerned about climate change than Americans, surveys have found. That is reflected in the rejection of not only air-conditioning, but also clothes dryers. You may find a clothesline at your rental instead. Energy shortages in recent years have also led to limits on power usage.

Older styles of architecture built to keep people cool have meant that only about one-fifth of European homes have air-conditioning, compared with nine-tenths of American ones.

“You leave the shutters closed when it’s hot. You open them in the morning to let the cool air in,” Ms. Neri said. “And then you put up with a little bit of discomfort, and that’s not the end of the world.”

And when there is A.C., don’t expect anyone to blast it. “Even when it’s on, it’s not ‘United States on,’” said Amanda Rollins, an American TikTok creator who has lived in Paris for six years.

She recently went to a movie theater where she said audience members were fanning themselves, a contrast to the deep freeze typical in American theaters.

And then there is the matter of what to wear. Even with the heat, it might be ill-advised to wear the comfortable shorts, T-shirts and sandals that some people wear to dinner or the theater in the United States.

“Here in Italy, people dress up to take the garbage down the street,” Stefano Lodi, general manager of the Hotel Brunelleschi in Florence, said jokingly. “You wouldn’t dare put on flip-flops.”

Some fashion faux pas are blaring — beachwear on a city street, cutoff shorts and crop tops at a fancy restaurant. And the cost may be more than a dirty look: Upscale restaurants and even bars may turn you away for dressing too casually.

Mr. Lodi said he turns people away from the hotel’s Michelin-starred restaurant each summer because they arrive in shorts (despite the instructions to the contrary on the reservation confirmation). “They say, ‘It’s very hot; you should have told me,’ and we say: ‘Well, yes, we told you.’”

Other tourist spots, including churches, have dress rules. “No short shorts, no crop tops,” Ms. Rondinelli Huey said. In general, athleisure or sneakers may stick out.

In fashion capitals like Paris, heat doesn’t stand in the way of fashionistas.

“Even when it’s hot out, I’ll see French people wearing a long sleeve or a long dress or a coat,” Ms. Rollins said, adding that she rarely saw Parisians wearing shorts.

That is a contrast to the American style in hot summers: “We’re like as close to naked as we can be,” she said.