This video is really, really worth watching. TLDR: Jay Smooth makes an analogy between race sensitivity and oral hygeine. "Not being racist" is more like brushing your teeth than like getting your tonsils out. Our (all of our) prejudices are strong and reinforced 99% of the time just by absorbing the majority culture that we live in. Cultivating sensitivity toward minority groups, then, is akin to brushing your teeth every day.

...and it's basic civility, not rudeness, when you point out to someone that they have something racist/sexist in their teeth.