The music inside Paul’s Casablanca lounge was thumping on a recent night as sweaty dancers maneuvered under a disco ball. Outside, a line of would-be revelers looked longingly at the entrance. A green velvet rope was nearly all that was separating them from the good times being had inside.

That rope and Fabrizio Brienza.

As the “door” of the lounge, in SoHo, Mr. Brienza is in charge of plucking patrons from the line to enter. Only a choice few get in.

“I curate the vibe of the place,” said Mr. Brienza, who has worked at Paul’s for five years and estimates that on busy weekends he turns away hundreds of people who don’t fit that vibe. Which is defined solely by him.

Mr. Brienza is on the front lines of gate-keeping in a city that thrives on exclusivity, giving rise to power brokers around every corner.

In New York, co-op boards decide who gets to buy apartments, and restaurant hosts control who gets the best tables — or any table — at the city’s hottest spots. Admissions officers choose which parents can send their children to the fanciest preschools. Even fishmongers have their own seat of power, selecting which high-end chefs get the prime catch.

Mr. Brienza is among a handful of so-called doors who decide which revelers get to come inside various nightclubs and lounges for drinking and dancing.

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