Hosted by the New York City comedy collective Improv Everywhere, the No Pants Subway Ride is an annual New York City tradition where folks go pantless --together-- on the subway. Now in its 17th year, the group has just announced that the 2018 event will happen on Sunday, January 7th. If you're interested in joining in on the fun, be sure to sign up for their mailing list. They'll be sharing more information there closer to the event's date.
The event happens outside of New York City too, but Improv Everywhere doesn't specifically run it. People like you do. They write:
Once again we are encouraging folks in other cities around the world to stage their own No Pants Subway Rides on the same day. Regional organizers must fill out this registration form to have their event included (that form is for organizers only.) The week before the event we will publish a list of all participating cities along with links to Facebook events. Groups have staged the event on trolleys, light rails, and buses in the past, so don’t let a lack of subway system stop you! 60 cities participated last year. Check the list on this page to see if one happened in your city last year as preference will go to the prior year’s organizers...
Here's a look at last year's event: Full details can be found on Improv Everywhere's site.
(If you go, I want to see pix!)