I remember a superb one that Blue peter did about 25 years ago. They did a news report saying that scientists had invented a brilliant answer to droughts: a pill that converts to water under sunlight. Unfortunately, the lorry carrying the pills had crashed and overturned causing the pills to spill all over the road and as it was sunny, they had all converted to water, about ten times their actual volume, and caused a flood. There were photos of the lorry on its side in the road, and the street completely flooded.
Of course, the tablet was called: The Arfoo Pill (anagram of April Fool)
