Cycling is chock full of nicknames for riders, even if they have one sometimes someone here at the Café will coin a new one. One of the earliest ones from here that I remember is "evil Cricket" for Paolo Bettini who is fondly known in Italy as il Grillo, or the Cricket.
Alberto Contador became "The Accountant" because of a babelfish translation of a news story that contained his name, (I think.)
Tony Montana, aka Fabian Cancellara is almost self explanatory. Then he became Spartacus to his fan base, and was even rumored to have that name on his bike helmet.
My husband and I call Tyler Hamilton "The Muppet" because of his riding style.
Someone here at the Café coined the nickname "Bubble Boy" for Tommy Danielson, that gave me a good laugh. Another one I saw here the other day was "Mr. Excitement" for Levi Leipheimer.
When I was putting together my VDS team for this year I was reading rider profiles on Wikipedia (I was surprised at how many riders actually have a Wikipedia page) and saw that Heinrich Haussler's nickname is "Beans." Made me think I would not like to be riding behind him in the Peloton.
You can post your favorite rider nickname in this thread, or ask about why a rider has a particular nickname. Someone may know the answer.