Ad hominem

Ad hominem is a type of logical fallacy where a person or group of people attack the moral standing of another person instead of refuting that other person's arguments. Ad hominem is a fallacy because the character of a person making an argument, good or bad does not affect whether the arguments are logical or invalid. The character of the person arguing is irrelevant one way or the other. When a person's physical features are attacked that's even more irrelevant.

The links below gives a better explanation.