With temperatures climbing in Rio de Janeiro, specators lounge on the beach of Guanabara Bay on Wednesday during a sailing event. (Nic Bothma/European Pressphoto Agency)

From his paddleboard rental tent at the far end of Ipanema Beach, Paulo Vitor Breves has ample opportunity to observe the beachgoing Olympic tourist in his new foreign habitat.

Several distinct traits identify the gringo, he noted. Most foreigners pick up their trash instead of leaving it strewn in the sand. The women hide behind towels and awkwardly shimmy out of their bulky outer clothes. And that vast bottom half of the tourist swimsuit always comes as a shocker.

“Their bikinis look like underpants,” Breves said.

The beaches of Rio are governed by intricate protocols. Where to sit, what to eat, how to interact with your fellow half-naked man. When the world’s tourists come galumphing in for two weeks during the Olympics, smeared with mosquito repellent, wearing backpacks on their chests and sneakers in the sand, they are bound to be breaking several invisible and inviolate rules.

Rio de Janeiro is hosting the summer Olympics. Here’s why there’s reason to celebrate – and worry in Brazil. (Lee Powell/The Washington Post)

So let us stop pretending that we care so much about archery and dressage and take a stroll down Ipanema. We, of course, see the Brazilians, with their floss-sized bikinis and snug sunga shorts, but how do they see us?

“They drink. A lot,” said Alexandre Conceição, 27, who studies the tourists while tending to beach chairs and umbrellas at a stand called Barraca Mineiro. He is used to Brazilians enjoying an icy beer. But some foreigners “get so drunk on caipirinhas that they fall asleep and their friends have to carry them home.”

Cariocas, as Rio residents are called, may seem casual and carefree, their city a paradise for the no-shirt, no-shoes traveler. But residents have their beach-life rituals. They eschew the beach towel, as it’s too heavy and cumbersome and gets all gummed up with sand. They prefer the multi-purpose light cotton sarong that can be worn as a wrap or spread on the sand. The setup process for women preparing to sunbathe, with its elaborate bikini tweaking and adjusting, seems like performance art, as does the post-beach rinse down in the outdoor showers.

Cariocas don’t wear tennis shoes or socks or jeans to the beach. They laugh at goggles, and they avoid draping themselves in expensive jewelry or watches on the sand. They also respect the power of the South American sun, applying regular sunblock, and leave the farmer tans to the tourists.

“We can see the gringo from far away. Far, far, away,” said Natali Gama, a 24-year-old student lying next to a friend.

She motioned to a blond woman sitting next to them wearing a rather unsubtle green-and-yellow Brazilian-flag bikini.

“Of course, she’s not Brazilian,” Gama said.

Rio residents can often be spotted with their beach chairs moving like sundials, slowly rotating throughout the day to catch direct rays.

“Gringos always sit facing the ocean,” said Adriana Silva, 47, her back to the sea.

She and her husband, Marcelo Fischel, live just off the beach and come to the sand almost every day, sitting in the same spot, attended by the same coconut vendor. They generally enjoy the presence of tourists, with certain caveats.

“They bring cameras all the time,” she said. “We just feel sorry for them when they lose their cameras and their cellular phones.”

Brazilians often keep their beach possessions simple: water, sunscreen, sunglasses, cellphone, some money and the sarong, called a canga. When the tourists lumber in with a camping backpack or, it goes without saying, a fanny pack, they’ve been marked. Leaving those possessions unattended while one goes swimming is downright alarming to the locals.

“I was freaking out,” said Juliana Gravina, 25, a law student, as she recalled watching a group of foreigners leave a backpack on the beach and walk to the water’s edge to try altinha, the Brazilian game of juggling a soccer ball. “I went over there to tell them, come on, it’s not safe. Pay attention to your stuff.”

Theft has always been a concern here and has caused lots of problems throughout the Games. Two Australian rowing coaches were mugged at knifepoint as they walked on Ipanema. There have been reports of thieves impersonating the vendors who sell sweet tea or sunglasses or fried cheese, distracting a beachgoer while a partner moves in for the theft.

Unlike the sun-worshiping foreigners, oiled and supine, Brazilians tend to be up and about, engaged in all manner of athletics. They play at least three different versions of volleyball and dabble at soccer, surfing, boogie boarding, body surfing, skim- and paddle-boarding, and something called “fresco ball,” which is another paddleball variant.

“It’s a characteristic of the beach to stay on your feet talking, not lying down and sunbathing like the Europeans,” said Laura Perez, 51, a social science professor at Universidade Estácio de Sá in Rio. “People on the beach are on their feet, drinking a cold beer, conversing and eating a Globo biscuit.”

The aforementioned Globo biscuit was profiled in the New York Times last week, its “distinctive flavorlessness” compared to “an oversize Funyun minus the onion, or what you would get if you ordered a Cheez Doodle, hold the cheese.” The article prompted outrage on Brazilian social media and in the media, as citizens rose in defense of their bland beach snack.

“A foreigner speaking ill of biscoito globo is like a guest complaining about your grandmother’s cake,” one Brazilian tweeted.

Brazilians are well accustomed to absorbing waves of tourists. Rio’s white sand beaches attract foreign visitors all year, and even more when a major event rolls around such as Carnival, the World Cup or the Olympics. As hosts, they are proud of their reputation as welcoming and friendly.

“Norway, USA, France,” said Polyanna Moreira, a high school junior lying on the beach, listing the countries of all the new friends she had made during the Olympics, on the beach and out at the samba clubs.

“Italy,” her cousin, Penelope Tone, added.

“I like the tourists. I like to see the city crowded. It’s nice,” Moreira said.

But some Brazilians say that too much foreign attention can become a drag.

In nothing but Ray-Bans and his Calvin Klein sunga, Raul Vinicius, 25, was surveying the scene on Ipanema near Farme do Amoedo street, considered a gay-friendly part of the beach, with rainbow flags rippling in the wind. In his home town of Florianopolis, in southern Brazil, he said, it was normal to flirt at the beach. But in Rio, he’d noticed male prostitutes trolling for foreigners and the tourists also aggressively hitting on locals.

“It’s part of the game here,” he said.

Several Brazilian women said that tourists seem to think all cariocas are single and willing, which can get annoying. But some men said they are using the meat-market atmosphere as inspiration.

“I got an American haircut,” said Thiago Hins Fereria, with long locks somewhere between surfer and Rastafarian. “The Brazilian women only want the gringos.”

“There are going to be children of the Olympics,” he added.“The hospitals will be full in nine months.”

Dom Phillips contributed to this report.