
You seem to be looking for conversation where you have the 'advantage', or at least that is the preferred way. Say, for the sake of argument, you had a conversation with tw Christian , one was false and the other was preaching the same Gospel as the Apostles did. How would you tell the difference, and you should be able to as they act quite differently, especially in a pack, I mean group?

There is no verse that says all Atheists (or any other religion) are worse people than false Christians, it's quite the opposite.
Say the return is similar to us entering a room when we are already aware that we won't like anything we find in there. Once through the door who would normally be the first target, the closest ones or it might also be some trying to hide on the far side of the room and the closest ones are just brushed aside for a moment or two. With Christ's return, the ones who claim to be Christians (call Jesus Lord) are 'examined' first. If nothing else the magnitude will not leave you wondering who is behind the events, if the magnitude is less than promised it isn't God at work. That isn't a really dangerous view to anybody, if anything it is a call to 'potential Christians' to read all the fine-print before signing on.