Outside the O2 Arena in London on Monday evening, the hip-hop superstar Pitbull tore into a bowl of chicken katsu curry. A few feet away, Pitbull fumbled with an iPhone charger. A lone Pitbull checked his watch, and a conga line of Pitbulls rode up an escalator. Two Pitbulls were holding hands. Four more split a bottle of rosé.

The actual Pitbull — Armando Christian Pérez, a Miami native who steered a boisterous strain of club-rap to the top of the charts in the early 2010s — was backstage, preparing for the first of two performances at the 20,000-capacity arena. Waves of young fans have gotten in the habit of impersonating the artist at each date of his “Party After Dark” tour, paying special attention to his most famous, most hairless, feature.

“I’m pretty sure every party shop in London is sold out of bald caps,” said Jay McGillan, 19.

Mr. McGillan said he had visited seven stores and struck out, so he improvised by drawing a portrait of Pitbull’s sparkling pate directly onto the fabric of his white button-up shirt. He joined a line of fans streaming into the arena, one of them wearing a T-shirt that read: “Good girls go to church … Bad girls go to Pitbull.”

It’s boom times for the concert uniform, a relatively recent phenomenon in which fans coordinate on social media to wear sequins to see Taylor Swift and cowboy boots for Beyoncé. (Jimmy Buffett’s Parrotheads were way ahead of the curve.)

But Pitbull mania is an outlier in terms of its outrageousness, its lack of obvious sex appeal and its uniformity. To wander among the Pitbulls feels like Halloween night, if Halloween had only one costume option and it was Pitbull..