In the eclectic fellowship of Bryant Park moviegoers, Loren Finkelstein is the Sheet Guy. That means that every Monday night during the summer, when classic films are shown in the green oasis of Midtown Manhattan, he wheels a suitcase with two dozen sheets into the park at 5 o'clock sharp.
Then, on behalf of dozens of friends who will arrive later in the evening, he and some comrades arrange the sheets near the screen - "Worst case scenario," he says, "is that it's not a square, but some crazy shape" - and then make common cause with their neighbors.
The goal is to prevent someone from plopping down to block their view at the last moment, which, in the case of the Bryant Park film series, is exactly 30 minutes after sunset. "We make sure all of the sheets overlap so that no one can seize a patch of grass," explained Mr. Finkelstein, 41, a genial film buff who works in computer support for a financial services company.
The HBO Bryant Park Summer Film Festival turned 19 this summer, only marginally younger than the median age of its audience. While it now has competition from other al fresco movie series in New York, Bryant Park holds the cinematic sweet spot - in the center of the borough at the center of the city - and has spawned its own obscure cultural traditions and iron-clad rules of etiquette.
No. 1: Take off your shoes. It is all right to walk barefoot on others' blankets, but those who fail to remove their footwear will be dogged by shouts of "Shoes! Shoes!"
"People get testy about their blankets," said Jessica Brunacini, an environmental educator from Brooklyn.
The firmly established protocols allow several thousand people (with many, many bottles of pinot grigio) to shoehorn themselves into a one-acre lawn and get along on a steamy summer night. It is, perhaps, the one place in Midtown where the peculiar admonition "I'm stepping over you" is met with an appreciative nod.
The ritual begins hours before the movie, well before 5, as moviegoers wend through a security check and then line up on the park's perimeter. Park employees dot the lawn to ensure that no one jumps the gun. Then, at precisely 5 p.m., an official shouts, "The lawn is now open."
A collective squeal goes up, and in they run from all sides, sheets fluttering, baguettes jostling in tote bags: a rush hour to rival the one on nearby Avenue of the Americas. Staking out a spot is just the beginning, however, and woe to the novice who wanders off in search of provisions.
"If you leave your blanket, I give it 10 to 15 minutes and then I move in," said Christina DeNardo, a graduate student at Bank Street College of Education, explaining her impulse to upgrade her vantage point.
In mid-July, for "In the Heat of the Night," she was early and well equipped. She had arrived with a fellow student, Rachael Beseda, with brie, hummus, carrots, cashew nuts, popcorn, pita bread, crackers and sauvignon blanc. They even had a small wooden table.
In some ways, the hours leading up to the movie are the main event, a timeout in which friends and family members do things not on their to-do lists. Before the showing last Monday of "Airplane!," the distant thrum of bus brakes and car horns receded as the metallic buzz of cicadas rose and fell from the London plane trees encircling the lawn. A jet sliced across the sky.
As the park filled, people relaxed on fleece blankets, paisley throws, beach towels and plaid sheets. Naomi Warner, a college student from Queens, knitted a trivet with multicolor yarn. Dana Harris, a marketing intern, read the short story collection "In Other Rooms, Other Wonders" on her Nook. Hoon Lee, of Palisades Park, N.J., took a panoramic photo of the skyline with his iPhone.
Slightly more ambitious, Christie Yamron, a real estate agent from Manhattan, pulled out the game Scattergories and coaxed her friends (busy passing around a pretty floral flask) to play. Ms. Yamron came up with a winner for the category "Things in a Park" starting with the letter T: "Tipsy movie watchers."
All kinds of techniques to locate friends are allowed, from wildly waving to guiding them by cellphone.
Two well-established groups are known for their inflatable mascots, which serve as beacons for late arrivals. One is a cooler in the shape of a palm tree; the other is a blowup cactus (known to aficionados as Cactus Pete) that stands more than five feet tall. Balloons work too: before "Airplane!," two pediatric cardiologists floated a heart-shaped balloon to signal colleagues from NewYork-Presbyterian/Columbia hospital. But come movie time, all such obstructions, including Pete, must be deflated.
Going to the bathroom presents other challenges. At 6:45, the public address system came to life with some "housekeeping items," including the fact that after 7, the park's bathrooms near the library are for "ladies only" and men must then use the portable toilets on 40th Street.
The social mores become apparent as the crowds thicken. The last-minute lawn grab is especially anxiety-inducing, as latecomers try to colonize the ribbons of grass between blankets. Some are better than others at waving interlopers away. "There will be a couple of feet and someone will come, and I'll think, 'You know, I've been here for hours,' " Ms. Brunacini said. "But I won't actually say anything. I'll just give dirty looks. I tend to be passive-aggressive."
Just before showtime, however, any tensions are released when the audience jumps up and starts hopping and clapping to HBO's traditional theme music, as a promo appears on screen. It is a one-minute boogie whose origins are unclear but that has gone on for at least a decade.
Once "Airplane!" finally started on Monday, the chatter that had grown in volume with the successive pours of a thousand wine bottles fell to a hush. People actually watched the film, laughing in unison - just like at the movies. At least most people.
Some checked their phones nonstop. Others fell asleep. A few ducked out early. "It's not about the movie," Mr. Finkelstein said. "It's about having a picnic in the park."