If you really want to get to know your fellow church goers, you’ll have a hard time passing as an atheist for long. Sooner or later you’ll be asked to lead a prayer, give ‘testimony’ to when you ‘got saved’, be tested on your working knowledge of the Bible in some way. And at a catholic church, there’s generally less close community beyond glad handing, but there’s a lot of ritual and recitation you’re expected to follow along with. On some level true believers will always be pinging you to determine your authenticity.