I prefer to go by this definition of racism:
"Racism, however, describes patterns of discrimination that are institutionalized as “normal” throughout an entire culture. It’s based on an ideological belief that one “race” is somehow better than another “race”. It’s not one person discriminating at this point, but a whole population operating in a social structure that actually makes it difficult for a person not to discriminate."
Racial slurs not backed by institutionalized racism are just laughable. For instance if someone called me "Cracker" I'd laugh about it since there isn't a huge past history of people lynching, raping, and harming my race while they chant "Cracker".
You can't say the same about the N-word however.