The word "racist" and its conjugations does not appear in the English language until the 1920s - see Peter Frost's cultural history [0]. If you asked Shakespeare if he was a "racist," he would not know what you meant.
"Racist" is essentially a term of abuse which no group or party has ever applied to itself. Like most such epithets, it has two meanings - a clear objective one, describing a person who fails to believe in the anthropological theories of human equality which became first popular, then universal in the mid-20th century; and a caricature of the vices, personal or political, typically engaged in by such a foul unbeliever.
I actually like the answer given by Steve Klabnik above [1]. To call Steve a communist is a serious personal insult, and you can get banned for it [2]. However, Steve reserves the right to call himself a communist, or not, as he likes. This is actually kind of cool...
[0] - http://www.unz.com/pfrost/age-of-reason/ [1] - https://news.ycombinator.com/item?id=9676630 [2] - https://news.ycombinator.com/item?id=9676861