A CAUTION TO READERS: Objectionable language is discussed in this post. Those of you with delicate sensibilities may wish to give it a pass.
One of the linguistic aspects of the George Zimmerman trial is the dispute over the meaning of the word cracker. Some observers call it a racial slur, while others say that it is an affectionate term for a native Floridian.
I suspect that Trayvon Martin, in referring to the man following him as a "creepy-ass cracker," was not being affectionate toward a native Floridian, but neither do I think that cracker should be ranked among vile racist terms, though some dictionaries label it "racist."
Cracker is surely derogatory, and always has been as a label for poor white residents of the South. The earliest citation in the Oxford English Dictionary is from a letter of 1766 from George Cochrane: "I should explain to your Lordship what is meant by Crackers; a name they have got from being great boasters; they are a lawless set of rascalls on the frontiers of Virginia, Maryland, the Carolinas and Georgia; who often change their places of abode."
The boasting comes from an earlier sense of the word from the sixteenth through eighteenth centuries, when is was a term for a braggart or liar. (Thus the common belief that the term derives from cracker barrel is merely a folk etymology.)
My sense is that cracker as a slur is akin to rube, bumpkin, yokel, or hillbilly (which I occasionally heard in the variant hill jack when I lived in Cincinnati).* I leave it open for discussion whether it is more or less derogatory than the twentieth-century African-American ofay for white people, which appears to have fallen into disuse.
Should you call me a cracker, you would be spot on. I descend from several generations of not-particularly-prosperous white people in Fleming County, Kentucky, one of the counties included in Appalachia, and I myself am about as pasty white as it is possible to get this side of albinism.
Moreover, I have been called worse.
*For a bona fide racist term, you should probably look for white as an adjective modifying a polysyllable.