Threat of death.

And if I get much older, not even that lol

I'm in the closet as an atheist because I'm a teacher, and the culture of faith and belief has permeated the two schools at which I have taught (I don't talk about personal religious stances at all). I know of one teachers at my current school who was openly an atheist, but he is now retired. I've spent 15 years working to teach honors classes, and many of the students in those classes transfer from private religious schools. I fear certain students refusing to engage at all in the class or with me if I come out atheist, and then I will have problems with parents, etc. I just don't want to deal with it.

Growing up in a time when going to church was almost mandatory for people in a small town, I would say several. To my surprise, we quit going when I was fourteen. My father was almost always ahead of his time when it came to social issues.

Nearly all of them.

The Spanish Inquisition

Attending church is still a good social activity. Even if you're not a believer. You just have to find a church where the members aren't too over the top crazy. That's the hard part.