The polite answer is that an Atheist doesn't believe in a Deity...

Well I'm an atheist and I see no reason to not believe in a deity. It is far more accurate to say that I don't know whether there's a deity or not. I can hardly leave it at that, though, because that sounds like I'm undecided in an on-the-fence way. Au contraire. I've decided that the possibility of the existence of a deity is so infinitesimally small that I can ignore it for the purpose of how I choose to live my life. I've come to that conclusion by considering evidence. There's a chance I could be wrong. I'm an atheist because I see that chance as being about as likely as the tenth planet of Proxima Centauri being made of green cheese. It's an assertion that cannot be disproven yet for which there is no evidence.