On HBO’s “Curb Your Enthusiasm,” Larry David plays himself. Ted Danson plays himself. Richard Lewis plays himself. So it’s easy to assume that J.B. Smoove, who plays Leon, Larry’s motor-mouthed, freeloading roommate, plays himself, or at least a close facsimile.

But that turns out to be backward. “There is a lot of Leon in J.B.,” Mr. Smoove said, “but there is no J.B. in Leon.”

To illustrate, the 54-year-old actor, who was in the Diamond District of New York on a frigid Wednesday afternoon, pointed to his custom three-piece gray suit, black fedora, two-tone Hugo Boss shoes, silver tie clip and silver pocket watch.

“Leon couldn’t wear this,” he said. “Leon would spill gravy on it or something, you know.”

Mr. Smoove, who was in town to promote the show’s 10th season, wanted a gold pocket watch for his collection. “You know what, pocket watches are a lost art,” he said, “so what we got to do is bring this genre back to the fold. Style, I think, is something that refines you.”

As Mr. Smoove walked along West 47th Street, his fashionable figure cutting through the tourist-mobbed sidewalks, he went on and on about his love for analog timepieces.

“Everybody looks at the time on their phones now,” he said, free-styling in a staccato patter that sounded, OK, more than a little like Leon. “When the apocalypse happens, your phone is going to be worthless. You better have a watch on, or a pocket watch, or you better know how to read the sun, because if everything shuts down, none of this is going to work. Money is going to be worth zero if everything goes to hell.”

Trying to settle Mr. Smoove on any one conversation topic is like trying to capture a hummingbird with a kitchen strainer; he dips, he dodges, he flutters, rarely hovering in any single place for long. He only seemed to pause his Leon-esque flights of free association when fans stopped him on the street. “Hey brother, how are you man?” Mr. Smoove said to one man who asked for selfie.

“I’m the unofficial mayor of New York,” said Mr. Smoove, who grew up in Mount Vernon, N.Y., just north of the city, and keeps an apartment in Brooklyn Heights. “I could be the coach of the Jets, the coach of the Knicks. I could be the mayor. I could be an abundance of things here in the city and get away with it, too.”

This is not to say he doesn’t like Los Angeles, where he spends much of the year. “I love L.A. because I can do things that I can’t do here,” he said, pausing in front of Jewelers on Fifth, a sprawling, fluorescent-lit emporium filled with booths dripping with diamonds and gold. “A lot of people don’t know this, but I’m an R.V.’er. I freaking love it. Outside of traveling and acting, I think you need something to ground you, and R.V.-ing is life to me.”

He has a 39-foot Damon Outlaw that sleeps 10 people, with five televisions. “I’m not saying I’m a rough-it kind of guy,” he said.

He ducked into the emporium to see if anyone was selling pocket watches. The shouts came immediately: “Hey, J.B. Smoove!” “Last week’s show was crazy, man!”

Mr. Smoove, too, is pleased with the current season of “Curb.” “I’ve been on the show since season five, and the first episode is always the show where Larry plants seeds, and this year he planted so many seeds, he had like five or six story lines going.”

He was a huge fan before he was cast. When he was a writer for “Saturday Night Live,” his wife, Shahidah Omar, told him one night: “You’re going to be on that show because you say crazy stuff all the time, and I could see you and Larry together.”

Not long after, while visiting Los Angeles for a friend’s funeral, his agent told him he had an audition for “Curb.” Cosmic, right? But to Mr. Smoove, that’s just how the universe works. “I always think about time, and how the world is moving,” he said. “I always wonder who people are in their past.”

And what better way to capture time than on a vintage pocket watch. It turns out, they are hard to find in the Diamond District. After browsing dozens of booths, Mr. Smoove finally spotted one gleaming in a glass case. He leaned in to inspect it. It was gold, yes, but very petite, possibly a women’s, the vendor suggested. “Oh, I want a big man’s one,” Mr. Smoove said.

He slipped outside and walked a few doors down to another huge jewelry emporium, the Diamond Exchange. Pay dirt. A corner booth called NYCWatchmaker had a several prime vintage models on display. With the care of a surgeon, the booth’s proprietor, Harris Freedman, reached into the case and presented Mr. Smoove with an open-faced gold Patek Philippe from the 1950s that cost $6,000.

Mr. Smoove nodded approvingly. “Wow, beautiful,” he said. “It’s a nice, clean watch.” But he was in the market for a pocket watch with a dial cover that he could snap shut with authority. “It’s like people who got to be really good at the old cigarette lighters — click, click, click,” he said, pantomiming the gesture with flourish.

He loves those little retro flourishes. When he was in London filming “Spider-Man: Far From Home,” he would whip out his pocket watch with theatrical flair. “Everyone thought I was British,” he said. “I had my little topcoat on, would tip my hat at the ladies.”

Stooped over the case, Mr. Smoove admired the old-world craftsmanship a Breguet with a guilloche dial. Any purchase, however, apparently would have to wait, as Mr. Smoove took off on another a flight of fancy, about past lives, before heading toward the door.

“You know where I felt most at home?” he asked. “Rome. I swear to you, I felt like I lived there before, in another time.” Also, his legal name is Jerry Angelo Brooks. Angelo sounds Italian, he said, and “every time I pulled my passport out, every person that read it said, ‘Ah, Jerry Angelo, welcome back,’ ‘Jerry Angelo, you’re back.’ Isn’t that weird?”

“Man,” he said, as bundled in his overcoat on the chilly street outside, “I could talk all day.”