Continuity mistake: Missy's blond and blue-eyed like her mother, Mary, but in The Big Bang Theory, she's brown-haired and brown-eyed.
Continuity mistake: Younger Mary's a blond with blue eyes whereas on The Big Bang Theory she has brown hair and brown eyes.
Answer: Some people just have a dislike for someone that can't be explained. Could be as simple as the way he's dressed.