It is the day of the 13th annual No Pants Subway Ride.
The ride takes place in countries all over the world, but it was started in New York City by the group 'Improv Everywhere' in 2001.
The event is always held in January, to make it even sillier to see people braving the elements without pants.
Participants are lucky this year that the weather warmed up this weekend.
The group is asking those taking part to get on the subway as they normally would, and when the doors shut at the stop before theirs, to take off their pants, exit the train at the assigned stop and stand on the platform, pantless.