This group, Improv Everywhere, does commando performance art pieces. Sort of like what happens on Trigger Happy TV, but it's not filmed for television. I've only read a few, but I can tell at least my musician friends that they must read Best Gig Ever, and then the Band Response. I also loved No Pants 2002 and the MP3 Experiment. Both made me very happy to live in a world where such things happen. Thanks to Agent Roberts for the link.