What is the significance of Bitcoin Pizza Day, and when is it celebrated? Today, at Consensus 2017, some people were talking about getting Pizza to celebrate Bitcoin Pizza Day. What is the  story behind  that, and when is it celebrated?
Bitcoin Pizza Day is celebrated on May 22nd. On this day in 2010, a BitcoinTalk member bought pizza in exchange for 10,000 BTC. This represents more or less the first known transaction using bitcoins for actual goods.

The original post: Laszlo announcing his purchase in 2010

The significance has been growing especially now, because... of how much that 10,000 BTC would be worth today.