The N word.
I’m 55, and grew up in the 60's midwest in a white northern middle class home. The word was used, casually, although never to a black person’s face. (Apparently my family liked keeping their teeth.) N****r-rigging, n****r-rigged, were common expressions for make-do work with not quite appropriate parts, just what was available at the time the thing was needed. People on TV were called n****r. Black people didn’t live in our neighborhood.
When we moved to California I suddenly went to school with more non-white kids than I’d ever met before, and the school was still majority white.
I came to appreciate the diversity, and now it seems strange to me to be in an environment without Black, Hispanic, Asian and Middle Eastern people. Needless to say, I long since kicked the N word to the curb.