My opinion is that using the word "nigger," in any context, does not make one a racist. The word itself is just slang; a colloquialism, if you will. The problem with the word is that it has, in the past, been adopted by particularly racist persons and groups, so much so that the word, when uttered, instantly aligns the utterer with the deep-seeded racist groups that purloined the word.
An irrational fear or hatred of other races is what makes one a racist, not the language one uses. Witness:
Example 1: "Africans are sub-human mud people."
Example 2: "That nigger's got a nice lawn."
I see that one of the above examples is clearly a racist statement, inasmuch as it is a falsehood meant only to disparage a particular race based purely on one's irrational and unsubstantiated hatred of that race. I see the other as merely an example of American English colloquial speech. It's not about the words; it's about the motivation to use the word.
In [b]norman74[/b]'s offered example, when a person pisses you off and you scream "Hey, nigger!" as an open exclamation, I for one do not see that usage as being particularly racist. The word, though, does have maximum effect, much more so than, say, dago, spic, Mick, beaner, cracker, kike, fag, cunt, bitch or any number of colorful words, but only because, as I offered before, the word was pretty much used as a trademark to identify racist extremists in the past.