h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

The Chinese hierarchy has learnt nothing about communication technology in 25 years. The demonstrators' tents have finally been cleared from the area round the government buildings in Admiralty and the Chief Executive has told the citizenry to support local trade by going shopping in Mong Kok (which means busy place!) So, literally thousands of protesters are marching up and down with their yellow umbrellas chanting "We're going shopping. We're going shopping."
Hong Kong is a place where most citizens have at least 2 mobile phones, ideal for a flash mob.
Twenty five years ago the mayor of Shanghai smugly said that he'd managed to keep troops out of Shanghai and told the citizenry to go home and behave themselves. They promptly changed into white shirts and black armbands and held a funeral - about 10,000 of them in rows of 10.