It isn't. This is a made up word. There is NO word for that part of the body. It's a myth, used just because it SOUNDS like penis.

Because it's shaped like a hot dog or wiener.

Wenis (also called weenis) is a rare slang word. It is mostly popular with medical students. It means skin (or fatty portion) hanging off of an elbow, the rough patch of skin on elbow, or the tough skin enclosing the elbow. http://www.urbandictionary.com/define.php?term=weenis Another variations of it are "weeniz" or "weenise": http://www.urbandictionary.com/define.php?term=weeniz The excess (usually wrinkly) skin of the elbow. http://www.urbandictionary.com/define.php?term=weenise weenis envy: The deeply jealous feeling you experience when someone stretches their arm out in front of you, and pulls down their weenis (the flap of skin that covers the elbow) showing that it's bigger than yours. http://www.urbandictionary.com/define.php?term=weenis+envy Wenis is a type of flower in the shape of a weener. It was first discovered in Egypt roughly in 2500 BC. 'Wenis (or Weenis)The skin upon the end of the elbow. Also referred to as the funny bone of the elbow. 'WenisThe skin upon the end of your elbow. It is also referred to as the elbow's funny bone. http://uncyclopedia.org/wiki/Uncyclopedia:CVP/archive4#Wenis http://www.definition-of.com/weenie wenis: Used to replace any word. Example: Slow down, here comes a wenis sign. (stop) I'm going to punch him in the wenis. (face) Why don't you learn how to wenis! (drive) http://www.slangsite.com/slang/W.html