Granted
The year is 2013, world pizza day, after a lot of advertising by a number of major pizza chains across the world in the months leading up to pizza day. As a result the holiday is celebrated by a large amount of people. it goes down a sucess.
Over the next few years pizza day slowly grows, gaining it's own traditions. Soon it becomes a globally recognised holiday.
2015, a week before pizza day, a number of pizza chains group together and form a new currency: the pizza. Following the introduction of the pizza as currency it proves to be a sucess. within 10 years the entire world adopts the pizza as currency.
2017-2026 world obesity rates rise due to the fact that the world's main currency is also a rather fatty food.
2026 due to the widespread obesity, farm workers are in high demand. Due to the lack of labour the world stocks of grain plummet. This is followed soon by the world stocks of flour
Late 2026 massive deflation, noone can obtain any pizzas, the world economy crashes.
2027 due to the widespread failiure of the world economy there is panic, looting and widespread rioting, the world population drops by 40%.
Pizza day 2028 the holiday is re-instated by the survivors to remind them never to repeat the past, this time it is not a day to eat pizza, but instead it is a holiday to banish the sins of those who make and enjoy pizza, all those who cold be proved to have celebrated pizza day prior to 2013 are put to death by firing squad. Due to the survivors still being largely obease they are unable to hold eir aim steady and most of the guilty are shot in non- lethal locations, they are not treated and suffer and die slow agonising deaths from their injuries.
I wish i haden't just spent half an hour writing and cleaning that story up