I think i can understand this one

It can take a variety of forms on why someone could get more upset being called one then racism itself. For one, it can ruin your reputation if not a career, even if its not true or you are cleared, it has an ugly amount of thought attached to it for some people. You can get angry because your thoughts may be being misused or taken the wrong way, even if you did manage to word rather horribly your position, it can be very offensive to a person to be called a racist overall if you are very much against it, but still are inclined to tackle issues related very much so. For some people, being part of a culture may require one to accept things others may find racist, but to you are important positions to hold, or you may have experience that leads you to racist thought, like profiling, but you dont hold it as being racist, and then are offended by the accusation. Then you also need to account for what the person, or persons on the other end hold as being racist, but that would be off topic i guess, being its not as clear cut as it should be to me sometimes, and even that statement could be called racist, simply because i dont understand all of what racism covers of what is deemed racist by a giving individual or group of.
Overall to me you just have to take into the account of the individual and the simple concept of relativity that may exist in that persons perception, thought whatever word you may like to use there. So i doubt my opinion to fully cover it, or even hit the head of something that may sound like it makes sense to everything about it, though really does not answer the question fully or at all.
For instance, a collage football game commentator, cant remember details clearly, was canned when a remark he stated became more well known. He made a comment when a running back was making a big run, "look at that monkey go" or something along those lines. Now if a community wants to make something like that into a racist statement, or such a term has a racial history to a community, i feel such needs to be made known, so understanding and peace may occur. At the time though, or even if it applies, biology had not yet come to the idea that humans in general came to be in africa, and more to the point, it would then be a racist term to me for people in general, regardless of ethnicity, if you do not like to be called a monkey. THis person, was also very well liked by the local minority community, and had much involvement with it also, and more to the point, i have looked at people, that regardless of race kind of looked like a monkey actually, white, black, hispanic, asian, etc... so the boundaries of what is racist is not always known and it grows, and consusion may exist within the demand for a better tommrow. The desire to build a better america in terms of race is also hampered by those that would use such for means of power gain, either politically or at work, etc, which could create more distain for those that would call someone racist, or racism in general being negative, which is something i agree with, it being a bad and or evil thing(racism), just to clear that up. Racism is also not something that is of heavy education really, in collage you might be required to take humanities courses, that may in detail actually allow a person to understand a great amount of it, or what all may or is racist, or might even be borderline, or how many people may even know whats racist against them, so education of the people is something to take into account too. I could go on, but i fear the post may be a bit long in the tooth by now.