How do you handle the situation of your kid being called a “monkey”

Obviously when done derogatorily, a bop or two are due, but what about in other ways?

My sister called my son a monkey because he got excited when getting bananas. I know she wasn’t thinking in a bad way, but I sternly told her that we do not call my children monkeys, even jokingly or playing.

She got mad, saying she didn’t mean anything by it but i’m making a big deal out of nothing.

A little back story, even tho she is mixed herself, we were (separately) adopted into a white family, still live in a tiny conservative town and she has never really had “real world” experience.

How do I explain to her the importance of this? or am I really being too sensitive?