EDJ said:
^I HEARD IS CAUSE WHEN YOU SNEEZE, YOUR HEART SKIPS A BEAT OR STOPS OR SOMETHIN'.
Use of the word 'God' in surprise situations by athiests is based on the existing and extensive paradigm surrounding religion. Or, if you like, it's just one of those things people say.
I have a strange saying with my uncle - whenever he leaves my house, we either use the phrase - 'see you later, God bless you!' or, alternatively, the phrase 'see you later, satan fucks you!' - again, it has no real meaning whatsoever, but it's just something that's developed over the years and now I don't even think about it.