Extremely offensive. Not because ethnics so much dislike being called names, but as in all things, they're just not as good at whites as inventing good racial slurs. After much time and effort the few slurs that have been created to disparage whites include such underwhelming insults such as "whitey", "honkey", "cracker", and "skip". It is particularly outrageous that whites are merely amused when they're called a honkey.
Person who nursing a titanic hatred of humanity, and being unable to source any refined plutonium, resigns themselves to a more traditional form of creative expression.