My aunt's old greyhound actually was, uhh... dog racist, I guess. I don't mean towards humans, I mean other dogs. He'd happily interact with other greyhounds, doing all the usual dog greetings, but the less the other dog looked like a greyhound the more likely it was that he'd awkwardly ignore them and refuse to engage. Whippet? Cool. Lurcher? Ehhh, cautiously acceptable. Labrador? Absolutely fucking not
He was an ex-racer that my aunt got from a shelter, and he had clearly been through a lot before that. He got a good retirement with her though