You're in America so you don't care. So am I, and so don't I. But I remember posting about this a year or two ago when a group called Improv Everywhere gyrated in the windows of a store, a store which was decidedly NOT in on the prank. In this case the Liverpool train station, or tubeway, or whatever the hell they call it across the pond, was a co-conspirator with T-Mobile in making a production
out of thin air.
They call it flashmobbing.