your penis becomes erect (when seeing a hot lady) and then curls like a monkey's tail (hence the name) when it sees a repulsive ugly women.
if the woman is ugly enough, your penis will assume the monkey tail position and never ever creep back out into the world as a regular working penis again. It happened to me and I sued the woman for being ugly.
Wilger: This thing? It's my monkeytail beard!