I've heard about it so many times that I finally looked up the thread on bitcointalk. At the time Bitcoin was trading for pennies and "laszlo" a user on the forum thought that it would be cool to get some pizza for Bitcoin. It's a trade that will be remembered for all time! Take a look here: https://bitcointalk.org/index.php?topic=137.0
Below is a picture of the actual 10,000 BTC pizza
Oh, by the way, are you looking for a decentralized exchange?
Try https://bitshares.openledger.info/?r=sttcnstnc
Made by the creator of Steemit!