This is why deeming words offensive is problematic. As long as mean people exist, they're going to keep coming up with new ways to use words offensively.
I read somewhere that the phrase "mentally retarded" was introduced so health professionals could to avoid using words like "moron", which had developed a stigma thanks to the public using those words as insults. And hey ho, now "mentally retarded" is offensive because the public did the same damned thing to it.
On a quasi-related note: When I was a child, my parents had a friend who raced sled dogs. He used the word "bitch", he used it correctly, and he didn't have a problem with saying it in front of children because he was not saying anything offensive.
As you might imagine, my parents had to very delicately explain to us kiddies that we should not add that term to our vocabularies.