The faulty assumption that a person's argument (or idea, product, or person) is invalid or untrustworthy simply because of his/her genetics (racial, geographic, or ethnic origin).
Example: Mr. Spagnolo is a southern Italian Cornish Yooper. They're all a bunch of weirdos! There's no way I'm listening to him!
Example: President Trump: "I have had horrible rulings. I have been treated very unfairly by this judge. This judge is of Mexican heritage. I'm building a wall, OK?"
This logic is faulty because the judge, an American, may or may not have Mexican heritage, but none of that preclude the judge from being fair. This is similar to a Circumstantial Ad Hominem.