It's the annual 'No Pants Subway Ride' and groups are celebrating here in Chicago and around the world.
The organizers call it "absurdity for absurdity's sake."
Organizers from Improv Everywhere planned a Chicago edition of the subway ride and made a Facebook event page for those who wish to participate.
Roughly 175 people participated Sunday. Many met up to begin their ride at the Loyola station along the CTA's Red Line.
The 'No Pants Subway Ride' started in New York City in 2002.