One from Antarctica, one born on Antarctica, or anyone in reference with a word starting with "A". For example, "asshole", "atheist", "antagonist", "anti-pong" and "adventurer". True Antarcticans are rare, in that they are actually born on Antarctica, and it's probably safe to say that they don't exist except in silly comics. However, Antarcticans that are of one or more of the above traits are much more common than any person born on Antarctica.
"Silly Antarctican, no shit for you."
"Have you read that new Antarctica! comic?"
"You're such a fucking Antarctican..."