Go to a bar in the United States and order a Caesar. After the natives have beaten you for making up silly drinks that no one has heard of, visit the local grocery store and try to find some Clamato to make your own. Equally fruitless (clamless?).
Apparently, the Bloody Caesar is a little too close in kind to the Bloody Mary and the American tavern vernacular cannot allow such blatant conundrums.