I'm a Christian and all, but about the atheist thing, I don't do that. I don't 'avoid' them or tell my pastor about it. Maybe mention it to my parent. But then I just act as if they're any other Christian friend I have. I don't believe in making fun of others' beliefs, so it's basically like this dialogue:
Atheist: I'm an atheist.
Me: I'm Christian.
Buddhist: I'm Buddhist.
NOT
Atheist: Evolution is loving real!
Me: Lol you're funny bro
Buddhist: Buddha have mercy on all of you!