Although OMG is a new-ish social media abbreviation for it, "oh my god" has been a much used exclamation ever since I was a child. I remember my mother frowning on it, like it was some kind of swear word. It's interesting to think about the circumstances in which we usually speak this phrase. We say "oh my god" when we're surprised. We say it in the face of a stunningly gorgeous scene. We say it when something unthinkable happens. We sort of mean it when we say it. For the small text I used a line from the Mahabharata – see next image for detail.