The 2015 No Pants Day will take place May 01, 2015. No Pants Day is a prank that some groups have made into an annual event, happening on the first Friday in May. The prank is based on the premise of having people attend an event not wearing any pants resp. trousers. Participants are challenged to act as if there is nothing strange about not wearing pants in public.
The liberation of breaking a social taboo and seeing the reaction of people not aware of the event generally makes the event fun for its participants. Different groups celebrate it on different days of the year. There are unconfirmed reports that No Pants Day was first celebrated as early as 1985 or 1986. (From: Wikipedia)