Londoners have revived a hilarious tradition that's had travelers boarding trains without pants for two decades.

Dozens of pants-less individuals rode the Tube on Sunday as part of the annual "No Trousers Tube Ride," according to the BBC and The Evening Standard.

This year's ride was organized via Facebook by The Stiff Upper Lip Society, a London-based group, following a two-year hiatus amid the COVID-19 pandemic.

Improv Everywhere, the New York City-based comedy collective that created the international event, previously organized the event for 19 years, according to its website.

This is the first time the event — known internationally as the "No Pants Subway Ride" — has been held since the pandemic began in March 2020, the BBC reported.

The first "No Pants Subway Ride" was held in New York City in 2002, with just seven men participating in the inaugural event, according to Improv Everywhere's website.

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The participants, who pretended not to know each other, would tell those who asked that they "just forgot" their pants at home.

The prank eventually evolved into "an international celebration of silliness," per Improv Everywhere, with dozens of cities around the world taking part each year prior to the pandemic.

Not every "No Pants" event has gone smoothly, however. Police in N.Y.C. arrested eight people during the fifth annual ride in 2006, leading to increased media attention around the event.

Over the next four years, the number of "No Pants" participants skyrocketed from 150 to 5,000 — and by 2011, people in more than 48 cities across the globe were taking part in the annual event.

This year's event operated much like the others. Participants removed their pants at their respective stations and entered the trains in groups.

"For the remainder of the journey, sit in the Tube as you normally would. Read a magazine or whatever you would normally do," the event says on Facebook.

Participants were encouraged to wear "fun" undergarments, "but nothing that screams out, 'I wore this because I'm doing a silly stunt.' "

"Our aim is to make people laugh, not piss them off," The Stiff Upper Lip Society said.

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