Watch where you suntan this weekend. The prank group Improv Everywhere is planning a fancy beach flash mob in New York City where they’ve asked people to show up at the beach wearing black-tie attire. This will be the 4th annual Black Tie Beach, according to Sōsh:

The mission is simple: show up to the beach completely decked out in your fanciest get-up. Conduct business as usual, building sand castles, riding waves, sunbathing. If anyone asks why you’re wearing formal wear, reply that you just “felt like dressing up. The first rule of this flash mob is: you do not talk about the flash mob.

The location will be announced today [Update: Seaside Beach, Coney Island], more details at Improv Everywhere. Here’s a video from last year’s Black Tie Beach: