When called a racist, “So’s your old man!” is a not inappropriate response.
If it is a woman, I respond with, “I have more evidence that you have a secret life as a $20 street walking prostitute than you have that I am a racist.”
If it is a man, I respond with, “I have more evidence that you are a pedophile, that you get off sexually with little boys, than you have that I am a racist.”