I have noticed that I have no issues telling anyone that I am non-religious. I know they know that means that I don't go to church and don't practice any standard religion. No one reacts badly to my saying non-religious; at most they'll ask why. How I explain why depends on the person, I try to respond in a manner that I think they can listen to instead of tuning out due to extreme disagreement. For instance, if the person is very religious I start out by talking about being tired of how so many religious people are hypocritical. By the time I get around to saying anything that offends them they have agreed with at least half of my reasoning. With everyone else I just say that my reasons are quite complex but that the main reason is there simply is no evidence that any one religion has figured things out. If you get this far with someone; you can say 'atheist' pretty easily without them freaking out
I would never just walk up to someone at work or family gatherings and make a point to tell them I am a Christian back when I was one. Why would I do it now that I am an atheist? However, I do find it difficult to not be afraid to just come out and say atheist if I am in a situation where it is appropriate to be discussing religious views. In this part of the country a lot of, otherwise fairly reasonable, believers associate atheism with Satanism/evil. I don't know if this is something they picked up from church or if it is just a Southern misguided view based on lies circulated by evangelicals. But, it is something I have to keep in mind if I want to be able to discuss my views with someone in a calm manner.
I would use the term freethinker, but a lot of people don't know what that means and could be offended if you can't explain what it means before they jump to the conclusion that you are implying their mind is not free (which might be your view anyway). Nonetheless, you don't want to offend someone just by stating your views. I understand it is the other person's problem if they can't accept the existence of differing viewpoints. However, if I can control the conversation in such a way that I can speak freely without the other person getting offended; I prefer to do so. I think the more we can have a calm and open dialogue with theists the faster they will accept atheists/freethinkers as just another approach to viewing the world rather than something to fear due to false perceptions.
Basically, if you are around reasonable people...what is there to fear? You might have to lead into stating your views in order to create a foundation for the other person's understanding. But after doing so there shouldn't be any issues. The only people who would truly freak out are the fundamentalists and I'm pretty sure average religious people already think fundies are crazy anyway. Try not to let all the jerks/trolls/insane people on the Internet affect your view of how people react in the 'real' world.
I think that for most of us, our fear to be open about our views is unreasonable. I can tell people that I am pro choice in public without anything terrible happening. And this is during a time when, to many people, that is the same as saying I'm pro murder. If I can safely be pro-choice and pro-teaching evolution in this society, why should I fear being an atheist? With the exception of those who live in very backwards parts of the country, our fear to be open is not based on reason. As most freethinkers pride themselves on making decisions based on logic rather than emotions; I think we all need to objectively reevaluate why we think there is a reason to fear being outed as an atheist.