When God created Man, he decided that Man would have 20 years of an active sex life. So he said to Adam, "You will have 20 good years to procreate, so go out into the world and multiply." Adam acknowledged God's commandment, bowed his head, and stood in the corner while God spoke to his other other living beings.
God said to the Monkey, "I grant to you a sex life of 20 years too."
The monkey looked at God and said, "Us monkeys are very sexually active in the wild. Ten years would be plenty for us. Otherwise we might burn out."
Adam overhearing this, said to God, "If the monkey only needs 10 years, why don't you give Man his other ten?" God thought this over a moment and agreed and gave Man the monkey's extra 10 years. Then God turned to the Lion.
"I give you the Lion 10 years to multiple and bring offspring into the world."
The Lion looked up at God and said, "You know, God, us lions are quite lazy. We lie around a lot and aren't very active much of the time. I think five years would be plenty for us."
God thought this request over for a moment and agreed. Upon hearing this, Adam spoke up again and said, "Since the Lion doesn't need his extra five years, why don't you give these years to Man too?"
God agreed and gave Man another extra five years for his sexuality. Then he turned to the donkey. "Donkey! You're a big animal with a long gestation period. I give you donkey 20 years to have sex and multiply."
The donkey looked up at God and said, "God, us donkeys don't get around too much. We probably only need one year for this."
God shook his head in disbelief, but gave in and gave the donkey only one year to multiply. When Adam heard this he spoke up again. "Since the donkey doesn't need his extra nineteen years, give them to me?" God agreed again to these requests and so it was proclaimed:
MAN HAS 20 YEARS OF GOOD SEX, 10 YEARS OF MONKEYING AROUND, 5 YEARS OF LYIN', AND NINETEEN YEARS OF BEING A JACKASS!