Yesterday I posted my suggestion for an atheists crest. Today I have a good quote that I think every atheist should memorize to use whenever someone asks them why they don’t believe in god.
“I contend we are both atheists, I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.” …Stephen F Roberts
Of course, feel free to paraphrase so that it flows naturally for you.