I am sure that I make mistakes, and this is a problem for me because I am sure that I am being incorrectly judged myself. If I am at a grocery store on Sunday morning and I see someone in a shirt and tie, I assume that this person is on the way to or from some kind of church. It's a pretty safe bet, and one that is mostly harmless. So when I go to work on Sunday morning in my shirt and tie, I feel very self-conscious.
I certainly never go around telling people that I'm an atheist or correcting them when they say 'god bless you,' but I also like to be clear when the subject comes up. If I am a part of the atheist movement, then the least I can do to advance my cause is to represent godlessness honestly. So when I am seen at 7:00 am walking to my car wearing a tie, I feel a pang of guilt about the assumptions I've made of everyone else. And yet I'm probably right. I'm sure they're going to church!