Why do they keep calling them flash mobs? Flash mobs are the nice little groups that surprise everyone at malls and other public venues with cheerful songs and dances. Another good thing bastardized by the left.
Because they can't call them black mobs.
The origin was a story by SF author Larry Niven, about a world with cheap teleportation: something interesting would happen somewhere, the news would get out, and people would teleport in to see themselves. . .