Commuters were left baffled when hundreds of people boarded the London Underground in their underwear.
Many were seen riding the Tube in the capital without trousers as other passengers look bewildered and confused at what was happening.
However, there is a hilarious reason why.
January 8 is No Trousers Tube Ride Day and this year is the first time enthusiasts were able to participate since the pandemic.
Today was also the inaugural trouserless tube ride on the Elizabeth Line.
There is no formal membership needed, and all anyone needs to do to get involved is just taking the Tube without your trousers on.
The point of the day is to make people laugh.
The idea comes from New York where people started the No Pants Subway Ride in 2002.
The event's founders claim: "There is no agenda for the event apart from a desire to make others laugh and smile."
The idea then made its way across the pond to Blighty, where The Stiff Upper Lip Society gave it a home on these British Isles.
Ivan Markovic, the founder of The Stiff Upper Lip Society told MyLondon : “We're not raising money, we're not raising awareness – we're just creating a moment".
"So I think the philosophy is to create a scene. We want people just to smile, to have a positive reaction.
"And the problem is once you start, if you start trying to make a statement or raising money for any charity, someone will always find a reason to object to whatever charity that you choose to support.
"So it's just purely an abstract concept. We just hope to make people smile and to bring a degree of levity into their afternoons on Sunday."
The group has more than 2,500 followers on Facebook.
A post today reads: "Thank you to everyone who joined us and rode with the official group... I really hope you enjoyed yourself today."
