There is zero real world scenarios where someone who is communicating in English in the modern day, call someone an n-word and does not mean for it to be offensive.
You mean, you personally weren’t the target of an insult and you apparently are mystified as to why any other people’s feelings are taken into consideration
Nazi and KKK consider it proper valid word, the only one that actually expresses who and what they have in mind. Their goal is not directly to offend, just to express how they feel about some people.
As far as they are concerned, the worst offense against propriety you can do is to ... call them racists. That is totally always unfair.
Calling someone the "n-word" doesn't really need a lot of cultural translation to be considered offensive.