Once upon a time there was a sperm named Stanley who lived inside a famous movie actor.

Once upon a time there was a sperm named Stanley who lived inside a
famous movie actor. Stanley was a very healthy sperm. He'd do pushups
and somersaults and limber himself up all the time, while the other
sperm just lay around on their fat asses not doing a thing.
One day, one of them became curious enough to ask Stanley why he
exercised all day.
Stanley said,"Look, pal, only one sperm gets a woman pregnant and when
the right time comes, I am going to be that one."
A few days later, they all felt themselves getting hotter and hotter,
and they knew that it was getting to be their time to go. They were
released abruptly and, sure enough, there was Stanley swimming far ahead
of all the others.
All of a sudden, Stanley stopped, turned around, and began to swim back
with all his migh. "Go back! Go Back!" he screamed. "It's a blow job!"