This New York organization http://improveverywhere.com/ , in its own words “causes scenes of chaos and joy in public places.” I’d call it something like “low budget high impact public urban positive humor.” Probably their most famous “scene” was when over 200 people suddenly froze in the middle of Grand Central Station, holding the pose of whatever they were doing. You should see the video clips of the reactions!
I have to warn you, if you’re like my wife and I, you will end up spending hours looking at and laughing at their antics. So you can’t say I didn’t warn you. 🙂 To start your journey, I recommend a couple of our favorites: http://improveverywhere.com/2003/05/17/circle-line-tours/ and http://improveverywhere.com/2007/08/22/the-mp3-experiment-four/. Have fun.