What if a mulatto looked white and claimed to be all for the survival of the white race?
Are you really comfortable making fun of others this way? That seems a bit strange.
It was a joke. It was said out of context and you took it seriously.. Chill with the political correctness please okay?
I doubt some one of mixed race would want to say something like this at all. How would you feel if someone jokes about your race? I can imagine it would not feel too good.
A mulatto is half white, so it's possible that they would want to be white.
Why would you want to say that biracial people act superior, though?  You shouldn't assume that they are unhappy with who they are.  You could make people think you're racist if you keep talking this way.