Because of a few no-shows, there was room for walk-ups (or rather, passengers). “We’ll show you to your table right now,” C. K told Nicolas and Ana Brandstader, a brother and sister from Buenos Aires heading to Williamsburg who stopped and went wide-eyed as helpers rigged up another plank.

Paul Smith, a CUNY professor, encountered the meal on his way home to the East Village and was invited to join. “I had this fantastic lunch,” he said, “very exquisite. And then I thought, am I going to get arrested?”

There was no sign of the police or even a conductor, but officials at the Metropolitan Transportation Authority, reached on Monday, were not amused. “A dinner party on the L train?” said Charles F. Seaton, a spokesman for the authority. “No. Subway trains are for riding, not for holding parties.”

In deference to the authority’s rules, the hosts did not offer alcohol. This did not assuage Mr. Seaton. “No beverages at all with open containers,” he said.

At Third Avenue came foie gras en brioche, with pots of homemade port-and-raisin jelly. Guests scrambled for knives and salt cellars that slid around the tables. As the subway rumbled, water refills sometimes missed the mark, and C. K. got on his knees to stabilize the tables and proffer wet wipes. Other riders gawked or — this is New York, after all — continued staring ahead and listening to their iPods.

Under the river and out to Brooklyn, where, at the Lorimer Street stop, the soup got on: purée of ramps, poured warm from a silver teapot, over black garlic, morels and a prosciutto crisp. Among the guests was Helena De Pereda, who is helping open a members-only club in SoHo and was considering hiring A Razor, A Shiny Knife for events. “They wanted to impress me,” she said. “They got the job.”

Like some counterparts in the underground dining scene, Mr. Cirino and Mr. Castaño aim for a punk theatricality. Halfway to the last stop, in Canarsie, Mr. Cristaldi, who performs as Jonny Cigar and hosts an itinerant wine saloon, began reading aloud from a copy of “The Great Gatsby” that he pulled from the pocket of his bespoke suit. The subway luncheon was his idea.