Adrants points me to Krantman, which is, as a reader comment at Boing Boing says, an advertisement for a dutch newspaper.
They have done it in the style of „trigger happy tv“ („Comedy Street“ in Germany), only not quite so drastic.
But the principle is the same. Put a guy in the public an let him do silly things. Then film the reactions of the unaware people with hidden cameras.
I don’t know, if they really filmed this with hidden cameras and unaware people, but it does look like it.
Nice idea, and the fact that Boing Boing (and also Adrants) mention it, should give it at least a small viral push.