Simple: 21 years of pizza shop experience (2 of those years done concurrently as I worked in 2 shops - one to help a friend.)
Then I got the email: For only $20 you can receive your bachelors, masters, or even PhD, and you don't have to take any classes. All based on experience. Well, it didn't take me long to realize that.. (j/k)
Pizza_guru got old quickly.. mr pizza didn't have any sort of ring to it... drpizza just seemed to work.
I'll be honest though - I'm sick of this nickname.
I'd rather be "The Master of the Red Crayon" again, but that's too long.