A person who actively engages in trying to get member of The Church of Jesus Christ of Latter-Day Saints to quit, or to stop non-members from joining. Anti-Mormons tend to be what I would call Bible Fundamentalists. They don't believe in any particular flavor of Christianity, but just that the Bible is infallible and that one should get all truth from it.
s alanet: As my defnition states, I (a real live Mormon!) only use the term anti-mormon for someone who actively fights the Church. As in seeking out Mormons and trying to get them to leave the Church. I think this practice to be more odd than bad. I don't see any of the things you listed as criteria to being anti-Mormon. I think it's great if you have strong enough religious beliefs to discuss them.

Jinmyo: Heh, I think he was joking. You can readily indentify a Mormon missionary by their tag.