I personally have no trouble telling friends if it comes up, never had a problem. But I do avoid it with people I don't really know, because I really have no interest in discussing it. Example: someone talks about God, I'll probably just say "sure, whatever". If it's a friend, I'll just say I don't believe in that and things are fine.
I can respect people believing in a God, but I find it kind of nonsense. People usually justify it with questions no one can answer. Were it any other topic with the basic premises (I don't know X, so Y is definitely possible!), people would see that as a lazy, dumb answer. When it comes to religion, people don't do that and justify it with faith. I guess that's what faith is, but I don't get why we have such a leap of faith in this topic alone.