1) "Nazi". It's sad because there are historical lessons to be learned from World War II and the rise of Nazism. But the term gets overused so much in politics, that just about anyone invoking the term is grasping at straws because he or she cannot come up with a coherent argument. See also, "Hitler", "Fascist", and "the end of America/democracy as we know it".
2) "Must have hit a nerve". The argument goes that, because you are responding at all to a point, then the other person must be right. Does that mean the best bloggers are the ones nobody reads? See also, "Riled up" and "Must be scared".
3) "Troll." There are a lot of trolls out there who lurk on blogs and comment on just about every post. Some of them make pretty weak and immature arguments. Those people should be easy to smack down. Others actually make good points. Don't dismiss them out of hand just because they have the courage to comment on a blog that disagrees with their views.
4) "Racist." Unfortunately, racism does still exist in America. But not everyone who opposes affirmative action or disagrees with Al Sharpton is a hateful bigot. If you invoke this term, you have better damn well be able to back it up with strong evidence. See also, "KKK".
5) "Bias." It's true, the mainstream media has a liberal bias, and Fox News has a conservative bias. Get over it. They are both popular and represent a sizeable chunk of the American electorate. Don't ignore what The New York Times or Fox says. Sure, they represent a particular view, but they often make good points. If the point is weak, attack that, not the background of the person making the point.
Excellent points made by the Staunch Moderate