Well it's true, if you say you're an atheist, there's a good chance you'll get the cold shoulder from a lot of people who are retarded. If you're American at least, there is a huge stigma for anyone who flat out says they don't believe in God.
So, if you want to, just say you're an atheist. You'll be doing the right thing, for you, which is all that matters.
Just keep in mind, that there are a lot of people who, if given the chance to get to know you, would completely change their opinions of what atheism means to them. You may not get an opportunity to meet these people, or show them how lame their thinking is... the very people who's opinion you could probably change.
You just have to decide, if it's more important to define yourself by your lack of belief, or if you want to "fit in" and try to change the system from the inside.
If it were me, I'd leave the religion (or lack of thereof) out of it all together. Because it doesn't matter. Just like whether you're a conservative or liberal, in the grand scheme of things, really doesn't matter when it comes to meeting people and making friends. That's all surface stuff. So treat it like a surface issue... if you want to get caught up in labels, good or bad, then go for it.