Smile! You're on Candid Camera.

Context

This is the catchphrase for the long running hidden-camera series Candid Camera (created by Allen Funt), which first aired in 1960.

Before Betty White's army of Olds were pranking younger folk and before Ashton Kutcher was punking celebs on MTV, a guy named Allen Funt hid cameras and secretly watched people do stupid things.

After the gags were over, he'd approach them and—before having them sign a legal release—would reveal to them the location of the camera, saying, "Smile! You're on Candid Camera!"

Where you've heard it

You know when something really crazy is happening, and you look around you skeptically and ask, "Am I being Punkd?" Well, anyone over the age of 40 will do the same thing, but will say "Am I on Candid Camera?"

Also, the show briefly returned to TVLand in August 2014, helmed by Allen Funt's little Funt, Peter Funt.