Blond girl steps on an elevator and just to strike up a conversation with the man already on it says, "T. G. I. F.".

He replies "S. H. I. T.".

She gets a surprised look on her face and says, "T. G. I. F. You know... Thank God It's Friday."

He calmly says "S. H. I. T. You know... Sorry Honey, It's Thursday".