I never meet an atheist with good manners though
As my mother used to say, manners are a mirror, what you show, you often see in return.
My advice to you my friend, is work on your approach to general human contact. If you show kindness, and good manners to an atheist, you may find that in retrospect, you will be able to say you've met more kind and good mannered atheists. I have met many kind and meticulously well mannered people that consider themselves Atheists, and many rude and ignorant Christians. The only difference is that Christians by default, have the burden of expectation.