Haha, here are some pretty funny large scale jokes:
#11: UFO Lands in London
On March 31, 1989 thousands of motorists driving on the highway outside London looked up in the air to see a glowing flying saucer descending on their city. Many of them pulled to the side of the road to watch the bizarre craft float through the air. The saucer finally landed in a field on the outskirts of London where local residents immediately called the police to warn them of an alien invasion. Soon the police arrived on the scene, and one brave officer approached the craft with his truncheon extended before him. When a door in the craft popped open, and a small, silver-suited figure emerged, the policeman ran in the opposite direction. The saucer turned out to be a hot-air balloon that had been specially built to look like a UFO by Richard Branson, the 36-year-old chairman of Virgin Records. The stunt combined his passion for ballooning with his love of pranks. His plan was to land the craft in London's Hyde Park on April 1. Unfortunately, the wind blew him off course, and he was forced to land a day early in the wrong location.
#25: New Zealand Wasp Swarm
In 1949 Phil Shone, a New Zealand deejay for radio station 1ZB, announced to his listeners that a mile-wide wasp swarm was headed towards Auckland. He urged them to take a variety of steps to protect themselves and their homes from the winged menace. For instance, he suggested that they wear their socks over their trousers when they left for work, and that they leave honey-smeared traps outside their doors. Hundreds of people dutifully heeded his advice, until he finally admitted that it had all been a joke. The New Zealand Broadcasting Service was not amused by Shone's prank. Its director, Professor James Shelley, denounced the hoax on the grounds that it undermined the rules of proper broadcasting. From then on, a memo was sent out each year before April Fool's Day reminding New Zealand radio stations of their obligation to report the truth, and nothing but the truth.
http://www.museumofhoaxes.com/top100.html