I watched a news story on these Improv Everywhere folks. They like to do these kinds of stunts where there is no real 'victim' but instead everyone that sees them plays the part of the straight man. Their most famous work is:
Frozen Grand Central (http://www.youtube.com/watch?v=jwMj3PJDxuo)
but they've done a lot of other weird stuff too, like:
Cell Phone Symphony (http://www.youtube.com/watch?v=-LKbCGV8aH4)
No Shirts (111 Shirtless Men in Abercombie and Fitch) (http://www.youtube.com/watch?v=jdeBp8J0rqs)
No pants 2k8 (http://www.youtube.com/watch?v=bXB_DcuMv_E)
and more! :D