In any kind of conversation there are a few steps that should be taken before the serious digging begins. First, you should attempt to find common ground. There is a lot of common ground among everyone who lives peaceably in any society. And there are a lot of people who make hay by claiming that those people don't believe in something we hold dear. Typically, this is done for the purposes of group coherence. We are the people who believe you shouldn't barbecue babies. So, it is essential you find common ground first, by stating that even as an atheist you don't believe babies should be barbecued. They should be slow-cooked.

Next on the agenda is defining common terms, if only for the purposes of the present conversation. People, everyone can understand that how words are used is important. There are a lot of people who think that there is an exact one to one correspondence between a word and an object or an idea. These people, by and large, aren't worth talking to. So, if you ask, "What do you mean when you say, 'Christian?'" and they respond, "What do you mean, what do I mean?" because they can't imagine that anyone would have a different idea, and if they do they're wrong, then that is a person with whom you need not concern yourself. At least on this matter, they simply aren't interested in discussion.

Of course, a problem arises when that person is your millionaire grandfather who is paying for you got go to college... But that's a different matter entirely. If you are able to find common ground and agree on common terminology, then it is possible to have a civil conversation. It takes a lot of work by both parties to maintain a civil discourse, and keep it from backsliding into snide name-calling, labeling, and rude, clever tricks. And, some science is showing that that kind of mental work is actually taxing on most people. But it's the only way that anything is ever achieved.