Just wear a sign that says "don't speak to me". That's what I do - ha.
Why do people think it's ok to speak for me? Someone was claiming that spaghetti was "cultural appropriation" and disagreed because I'm Italian and I don't agree that it is.
It is wrong for people to speak for you. If they do .. Just ignore them. You speak up for what you believe and they can just deal with it.
"Cultural appropriation" is a joke.
Honestly, it is because you let them. If someone is speaking for you and says something you don't agree with, it is up to you to speak up and correct them.