Pure flash mobs, like the Grand Central caper, are organized via social media, on short notice, for no apparent reason. Think dozens of people in a crowded subway car, talking into bananas. The newer stunts are often polished productions billed as “random acts of culture.” The concept already has been co-opted for commercial purposes (most famously by T-Mobile), to hype upcoming events or to raise money. There have been mobs to protest the BP oil spill and to demand that Chicago’s mayoral candidates articulate their arts platforms. … It’s going to take some imagination to keep this trend from going south fast.