When religious people ask why you left your former church and became an atheist it might be a trick, then again, they just might be curious. Since then you’ve hopefully grown, a lot. You’ve also probably read a few books and blogs, watched some YouTube videos, listened to some podcasts, and given it a lot of thought. Your default position has changed and as such your reason for being an atheist has also changed. While it may have been because of your study of doctrine X and Y or how Brother A treated Sister B, but now it’s just because there isn’t any evidence to support an extraordinary claim of that magnitude.
The attempt to get you to go back to that often painful point when you left your world behind serves to make it so the believer doesn’t have to deal with the new, confident, skeptical you, but instead the old, unsure, unstable you that was so full of cognitive dissonance. It also seeks to make irrelevant, subjective issues like, “Have you ever thought that maybe you were just the wrong kind of Christian?” a valid issue and put you on the defensive, shifting the burden of proof to you in trying to debunk theism in general and a version of Christianity that you may have never even subscribed to specifically.
I’ve fallen for this before, but not recently. However it wouldn’t be hard to address. Redirect the conversation to where you are now. Firmly establish the current burden of proof you would require. Especially be careful not to fall for the trap of trying to defend your former church’s position as the “right” kind of Christianity, especially since they’re all wrong.