the best i've known was while i was stationed in Norfolk VA and two morning DJ's went on the air and said that Mount Trashmore (a garbage dump turned into small park) was filling with methane and was about to explode. well they did not realize that their station was the lead for the area's emergency broadcast system. other stations picked up on this and started saying the same thing. police, fire,and other emergency
services were out evacuating the area. i don't know how far this went, but i understand that after the FCC finished with several hundred thousand dollars in fines, they had no more urges for april fool jokes. this was the tommy and the bull show. johnboy and billy or bob and tom are nowhere near as funny.