What's the difference between an "atheist" and an "anti-theist?"

Well, the first answer is that the first word is in the dictionary, and the second one isn't. At least not in mine.

But if the second word did exist, it would more aptly describe the "atheists" I've come into contact with recently...it isn't as if they simply do not believe in the existence of God, or gods...they dislike, and are actually antagonistic to God, or gods. They are against God.

This confuses me.

I mean, it's like the difference between an "amoral" person and an 'immoral" one. In the first case, the person simply doesn't care about morality one way or the other. In the second, however, the person understands morality, but acts contrarily toward it. See what I mean?

I guess my question is this:

Why on earth do "atheists" really give a bleep if so-and-so believes in God, or gods? By definition, it should make no never mind to them, one way or another.

'Course, I'm looking at this from the perspective of one who has read what atheists have written. It could be that those who claim to be "atheists" really aren't...and in fact simply can't stand God or those who believe in God, for reasons of their own. And that true atheists really and truly don't care.

If that's the case, though...wouldn't you think that the former might consider calling themselves something other than "atheists?" Because, you know, it just doesn't seem very honest of them...God love 'em.