I think nearly all of us have experienced this. I found it even worse in the United States than I do here in conservative, heavily Catholic Costa Rica.
Why are Americans afraid of atheists? The belief that god does not exist is not hard to come by these days, and appears to be growing throughout the world. But as a Pew Research Center report put it, when it comes to religiosity, “the US is closer to considerably less developed nations, such as India, Brazil and Lebanon than to other western nations...”
I have read some sociological studies that have found that greater economic equality and security is associated with decreased religious belief. Studies cite the examples of countries like Sweden and Denmark which have comprehensive welfare systems and quite low levels of religious belief. The USA on the other hand has great economic disparities and is quite unusual for a developed country in having high levels of religious belief. The poorest and most politically unstable countries in the world, e.g. those in sub-Saharan Africa, also have the highest levels of religious belief with over 95% of people professing belief in god. Researchers have proposed that religion provides people with a sense of security when they are uncertain about being able to meet their basic needs. In countries like Sweden and Denmark, people feel very assured of meeting their needs so religion loses its appeal. I wonder if this has something to do with fear of Atheism in the USA. People feel more insecure so they become more intolerant of people who do not share (and implicitly undermine) their belief that god will take care of them. That is, when atheists express their view that god is not real, religious people become troubled by doubts that atheists might be right, and they don't like it.