On Sunday, thousands of people in 60 different cities around the world took part in something called the "No Pants Subway Ride", including about 4,000 people in New York.

--The whole point is to freak people out.  Basically, you're supposed to get on a subway car with no pants on.  And if anyone asks you what's going on, you have to pretend you just forgot to put pants on that morning.

--The comedy group Improv Everywhere is behind it, and posted a montage of people doing it on the subway in New York.  (--Search for "No Pants Subway Ride 2013.")