1) People who insist that illegal immigrants should be allowed to gain all the benefits of being a U.S. citizen, without any of the drawbacks like paying taxes. If they want over here so badly, do it legally and/or become a U.S. citizen. Don't try to force us to change our laws so anyone can walk in and be showered with benefits without any taxes.
2) People who think that race should be a major issue in the presidential race. I'm sorry, but anyone who doesn't vote for Obama because he's black has some major problems. There are other reasons not to, but if his race factors in at all, that's just not right. You aren't helping America look non-stupid.
3) People who criticize movies and games harshly and reject your opinions when they haven't actually watched the movie or played the game. While it is possible to form an opinion by doing a lot of research to figure out the consensus (for example, I have a fairly good idea that Daikatana sucks, even if I've never touched it), you should not believe that your opinion should trump the opinion of someone who has actually interacted with the media being discussed.
4) People who think certain opinions are better than others. You know, funny thing about opinions...they're so subjective. For example, I like Mass Effect more than KOTOR. But if someone disagrees with me (provided they have an articulate argument explaining why they disagree), I don't really have room to tell them that they are "wrong", because they aren't. I can say I disagree and give my argument, but with opinions, you can't just dismiss someone's argument because "[person's] opinion is wrong."