I live in America and am surrounded by Christians.
Whenever I talk about myself to religous people, I want to say ,"I am an atheist". Do you say that? Is there a better way?
If they ask I simply tell them and don't worry about it. It usually starts a conversation.
Mostly I don't. I just politely refuse to visit their church services, throw away any literature they give me, or of push comes to shove just tell them I"m a non-believer and let them make of it what they will.
Just say it! Assuming that you've done your homework!