Seems God was just about done creating the Universe, but he had two extra things left in his bag of creations. So, he decided to split them between Adam and Eve.
He told the couple that one of the things he had to give away was the ability to stand up while urinating.
"It's a very handy thing," God told the couple, whom he found under an apple tree. "I was wondering if either one of you wanted the ability."
Adam jumped up and blurted out, "Oh, give that to me. I'd love it. Please, oh please, let me have that ability. It would be great. When I'm out working in the garden or naming the animals, I could just stand there and let it fly, it would be so cool. I could write my name in the sand. Oh, please God, let it be me who you give that gift to."
On and on he went, like an excited little boy who... well... had to pee. Eve just smiled and told God that if Adam really wanted it so badly, he should have it. It seemed to be the sort of thing that would make him happy and she really wouldn't mind.
And so, Adam was given the ability to control the direction of his urine while in a vertical position. He was so happy he celebrated by wetting down the bark on the tree nearest him and laughing with delight all the while. And it was good.
"Fine," God said, looking back into his bag of leftover gifts, "What's left in here? Oh yes, Multiple Orgasms."