An elderly couple was sitting on there rocking chairs rocking back and forth.©OFFICEJOKES.NET

When the woman whacked her husband as hard as she could right off his chair.©OFFICEJOKES.NET

Surprised and disorientated he said: "now why did you do that?" and she replied: "That is for 50 years of horrible sex".©OFFICEJOKES.NET

So he sits back down and thinks about it for a while, and pretty soon you hear another whack, this time the wife falls off the chair and soon, gets back up and says "what was that for?"?/p>

He replied, "that is for knowing the difference."