white people have this misconception that the n-word is a term of endearment. it's not.

babycakes is a term of endearment.
sugarpie is a term of endearment.
nigger is not.

slavery might not be happening anymore and jim crow might be gone—but when a white person uses the n-word casually, it's a reminder of the powerful oppression that once was (and still is, to a lesser extent).

the n-word is the only thing in our culture over which Black people have exclusive domain. all Black people know (and damn near all white people understand) that any use of the n-word by any other race other than Black people (Hispanics have been given somewhat of a pass with using the word) is socially unacceptable simply because the n-word has historically been used as a term for power and oppression over an entire population of people which literally lasted hundreds of years.

the use of the n-word amongst Black people is really a reminder to the dominant society that all the power that word once had—the dehumanization of an entire population for hundreds of years—has now been completely stripped away. using that word is the one thing a Black person can do that a white person cannot do in a social setting.