I know exactly what you mean, man. I recently had an argument with a Canadian friend of mine that started like this..
Me: No, I've only met a few of your friends. James, Phil and those Jewish people.
And the guy made this face like "whoa whoa, what is that? What do you mean "Jewish people"
I was like wtf, the adjective Jewish is a new synonym for retarded or smth?
People man