A man has been shipwrecked on a desert island for ten years. One day he spots a ship on the horizon. He frantically waves his arms and jumps up and down shouting, until he spies a rowboat being let down into the water from the ship.
About ten minutes later, the rowboat reaches the shore carrying a man in a captain's uniform. "Thank Christ for that!" says our shipwrecked hero, "I thought I was never going to be rescued."
"How long have you been here?" asks the Captain.
"Ten years, ten long years."
"Ten years? How have you coped all that time on your own?"
"Well, I'm quite a resourceful fellow, I've built my own house; there it is, over there."
"But ten years! Ten years without sex!"
"Ahhhh, well, that's not quite true" says the man shyly.
"About six months ago I was down here on the shore washing my feet, when I noticed an ostrich up the beach with it's head buried in the sand and it's ass facing me. Well, I thought it's been nine and a half years, so I crept up behind it and WALLOP!"
"Oh God, that must have been disgusting!" cries the shocked Captain.
"Well, it was alright for the first five miles, but then we got out of step."