Do you think the same about someone who says "I'm an atheist"?

It's a good question. I get annoyed at them, for sure, if only because they make an untestable assertion. However, most atheists, at least in the US, did not start out this way, so they at some point overcame the motivated cognition fallacy of sticking with the religion of their upbringing. If someone proudly says "I'm an atheist, I grew up in an atheist house" I find it little better then someone looking for supporting arguments for their parents' faith.