You're not really an atheist!
Surprisingly, some atheists, perhaps even most atheists, are really rather nice people. You might find that you can agree with them about nearly everything. As long as you avoid a few delicate topics, you wouldn't know that they were not Christians.
It is in these conditions that I have most often heard the words "You're not really an atheist", sometimes with a tiny question added on the end - "are you?"
In my case, I really am. We can even stray onto a discussion of some of the delicate topics if you feel brave enough. I could argue my point of view very robustly, but I would like to hope that I would have the sensitivity to tailor my comments to your tolerance levels. In the end, it doesn't really matter to me what you happen to believe in, as long as you don't impose your beliefs on me. That doesn't mean that I wouldn't like to share my point of view though.
Having said above that you might not be able to distinguish between an atheist and a Christian (providing you avoid a few hot topics), I think this says one good thing . . . about Christians.
They can't be all bad if they are so agreeable.
If you and I should ever meet and discuss those hot topics, I should warn you that I don't accept the bible as evidence of anything relevant to the existence of God or Jesus, but only as evidence of what people later came to believe. In order to know whether something is true or not, I do require evidence.
So I think it is safe to say that I really AM an atheist.
Last episode (2 weeks ago): I can't believe that you are so arrogant (or offensive).
Next week: Well, why don't you try praying?