I just read the thread, and it really does seem to be a conflict of world-views. From his point of view, Bob's "Make sure you thank God for His blessings" may just have been a jocular reminder -- something he might have said to anyone who seemed to be straying a bit. Perhaps it was akin to: "Make sure you look both ways before crossing the street!" - a bit condescending perhaps, but well-meaning. However, the street-crossing comment would probably annoy someone who didn't believe in the danger posed by automobiles to pedestrians; likewise, perhaps you were needled by Bob's 'reminder', and so took it as an opportunity to reaffirm your atheism (or an aspect of it) and your reasons for it. Bob (and others) in turn took your reply to be offensive, as it struck near, if not at, their core beliefs. (They might not have liked your use of the pronoun "it" for their god entity, either.)

I sympathize with your frustration at talking to fundamentalists on topics that seem innocent.

[By the way: Happy belated birthday! I had no idea you were born in June.]