With or without an organized event, this phenomenon probably happens in many subway systems around the world on a daily basis. But in London it’s an annual, official tradition. The 10th annual “No Trousers on the Tube Day” is back this weekend, and you can bet bare-legged commuters will be lining up in droves to ride the rails. For every Londoner who finds the practice distasteful, there are likely dozens of others eager to ride the tube with a renewed sense of freedom.

The first “No Trousers on the Tube Day” happened back in 2002, as the brainchild of New York-based improv group Improv Everywhere. Now, hundreds of Londoners take part in the tradition every year. The event begins at 2:30 PM on Sunday, January 13, with a gathering in front of the National Gallery. Everyone arrives fully clothed, but when the signal is given, pants are discarded and smaller groups are formed to board the tube. The event ends at 5:00 PM, when a huge after party at The Chandos pub commences.

If you can’t make the London half-nude escapade, the event also takes place in 26 other cities all around the world, from Dallas to Jerusalem. For more information on the event, and a full list of participating cities, check out Improv Everywhere’s official website. And to truly immerse yourself in the pantsless community, follow the Facebook page.

H/T: Secret London