Mine comes from my name, been throwing this around since I was 20ish, when I worked for a Little Caesar's Pizza doing pizza delivery.
Couple of us guys who were delivery drivers had a party after work, and some of them got drunk. One guy, Craig, looked at me and said, "You know, you look like...who's that guy from the Jolly Green Giant commercials? Sprout?"
Another one looked at me and in his smashed stupor, said, "Spr..frzz...Sprzzz..Sprzout!"
Next thing I know, everyone was using it at work, and it stuck. They even got me a keychain for Christmas that had Lil' Sprout, and it just kinda snowballed from there, so I kept using it...