If you're on the subway and see people with no pants, don't be alarmed. Each year more and more people participate in the event by stripping down to their skivvies and boarding subway trains for a ride, acting as if nothing had happened. 

It all started as a prank with a bunch of guys, but has now grown into an international craze with cities around the world participating. 

Photo: Getty Images

PHOTOS: New Yorkers Go Bare For The "No Pants Subway Ride" 2016