Unidentified group, wearing hoods and smocks, pre-1980 (Toronto Archives: Fonds 1257, Series 1057, Item 1216)
The first example of flash mobbing was this: The Hooded Jedi. Large groups of people (a.k.a. nerds) would conglomerate at public places dressed in hoods, preaching the word of Jedi-ism, accompanied by a local band (who just needed the cash). They have since disappeared from the public, but these are the same people who helped create our current Comic-Cons, so obviously the force is still with them.