Oh, I have doozy!It is also quite situational, so i will include back story.
We used to live in South Africa. There is a very, very bad word some people used to refer to black people (sounds worse than the Nword to my ears) and this is a word we *never, ever, ever* used. It is not a word my children knew, or would have known about.
One day, my 3 and 1 year old were helping our gardener sow some flower seeds. They are happily chatting to Uncle Simon about the "kaffertjies" (bad word for infant person of colour) and Simon is laughing his head off. (I am so thankful that he had the grace to laugh). My children were referring to Kappertjies, or as it's known to English speaking people :"nasturtiums"
Talk about a very uncomfortable moment!