McCoy is one of Spock's few friends. He invited him to his wedding for goodness sake. I don't think anyone can say McCoy hates Vulcans or thinks he is better than them. He doesn't agree that their general philosophy in life is correct to supress all emotions. Just as some people don't think its appropriate for women to wear a full burkha. He believes he has the sort of relationship with Spock that he is confortable with expressing his misgivings about the Vulcan supression of emotions especially in regards to Spock. Unfortunately McCoy sometimes make racist remarks which mostly Spock doesn't take seriously. If you take someone like Archer who probably did dislike Vulcans in general in the beginning of ENT, I can't remember him making a racist remark at all. Yet I'd say Archer and his crew were quite racist at the beginning of ENT. A lot more than McCoy. As T'Pol and the crew got to know each other their prejudices began to disappear.