As a kid (10 yrs old):
My 5th grade friend and I were playing with an electronics kit and he said if Ii didn't believe in Jesus I would go to hell. I just looked at him and said I didn't think so. He said uh huh. I said uh uh. And then we made the kit produce a siren sound and his mom came running afraid that the police would come. This was in Dacca, East Pakistan in the late 60's, they were Baptist missionaries. My dad is a geologist.
At work late 90's (43 yrs old):
I sneezed at my desk one day and an engineering co-worker at a cubicle across the aisle said "bless you". I said nothing and then as an afterthought joke he asked "What does an atheist say after he sneezes and you say 'bless you'?" He didn't know I was atheist and I don't know why he thought it would be funny but I said "I generally say 'Thank you'." He looked at me and then went back to his desk, my impression was that he was surprised, especially since I was his manager. From that day on I made it clear that I was atheist at work. Being a manager of the group may have stymied some discussion, but I don't think so. My mentions are matter of fact only when the subject comes up. I have one Catholic co-worker who will question and joke with me about it which shocks others sometimes, especially since I hold my own and joke back at her. But then I've had one come to me on the side and agree with some of my replies, Facebook rants or a comment from the news, especially when it concerns the Pope. These gals I'll often send science nerd news that shows them how the universe really works, trying to get them to see the real perspective of where we are in the universe. My morals are probably what has surprised them the most. Why am I so nice? Why don't I just want to rape and murder? What keeps me from trying that? Seeing the charity things I do used to just baffle them. I had to explain how altruism benefits a population and that it is natural for me to be good.
Meeting for breakfast the Baptist minister parents of my girlfriend's roommate, who happened to be a Methodist pastor at the time herself. (Yes, my lapsed Catholic, almost atheist, girlfriend lived with a Methodist pastor when I met her.) I knew I was going to be asked about my religion at this breakfast but had no prepared answer, mainly because I didn't know how it would come. Tarah's dad turned to me and asked how I was brought up. I said, "I was brought up pretty much straight." What did that mean? I don't know. That is what came out of my mouth. I then qualified that I didn't have any religion growing up and don't have any now. He was so amused by the "growing up straight" that the topic ended there. That forced me to have the "I'm atheist" answer ready to use. One of many moments in life I'd like to do over again but at least learned from.
At the airport in the 2010's:
Friends at the airport, fellow pilots, event volunteers who are also friends on Facebook have seen my posts about atheism. Three have come up to me on the side and said that they don't believe either. I hadn't read Why Atheists are so Angry yet so didn't encourage them to come out. I've read that now and also participate in the Santa Cruz skeptics meet-up group. That has honed my ability to discuss the issues of religion.
I am proud that I am atheist. I feel I dodged a bullet when I realize how much of my life was not wasted with religion. I've not once regretted expressing my atheism and have been pleasantly surprised by the agreement I've received, even quietly. But then I live in Santa Cruz county and work in Santa Clara county, pretty safe place to be atheist with bumper stickers and open discussion about religion. I've been flipped off a few times on the road but never had anyone in my face about being godless. Online is a different matter… but then I will comment on religious FB and Twitter posts without too much hesitation. Yes, I can be a troll. Not actively all the time, but it happens. I've been angry and I've been reasonable and patient. Maybe it has gotten through to someone on the sidelines.