I feel slightly offended when people say "GOD bless you" but it doesn't really bother me, because how would they know?
Unless they DO know and say it anyway. Then that's just rude.
And you don't have to say thank you. When people say Merry Christmas to me I say "yeaaa....Reasons Greetings." So I couldn't hold your lack of gratitude against you! Haha
Yeah, its a funny one. I'm from the UK where it's always "bless you" (nobody ever says "gesundheit" or puts "God" in front of "bless you"), but even as a Christian I used to say something like, "thanks - that was a close one, my soul nearly escaped that time!". A few people ask what you mean, but I was always surprised how many other people also knew the origin of the phrase and would then laugh with you at such a ridiculous idea. Think about it; how many people today - Christian or not - really say "bless you" because they are worried your soul will escape to the devil if they don't?! It's purely a cultural habit.
I live in the Netherlands and here it's "gezondheid" meaning health, same as German. I think that's also what most people saying "bless you" would say they mean - that they wish you well and hope you aren't coming down with pneumonia or something terrible...
I do NOT feel offended by any means when someone says "god bless you" when I sneeze. I feel that it is the intention of the person saying it to be of "good will" and "sincerity" when they say it - even if it's out of habit. And whether I believe in god or not. I'm more a tolerant Atheist than a militant one. However, When someone comes knocking on my door spreading their "so called "WORD", I politely say, "I'm sorry, I'm an Atheist". And if they do not accept that right from the get go - well, THEN we have a problem! LOL