Jack and Mack are both on leave from the Army and are heading to Jack's house for the break. Jack keeps telling Mack how great the girls are in is home town and how they are both guaranteed to score. After being at Jack's house for several days and not seeing a single girl around town, Mack asks, "Where are all the women you were telling me about?". Jack replies, "Well, mom says that they have all gone off on some sort of religious retreat and won't be back for a month. Don't worry though, because I know something even better!" The next thing that Mack knows, he's standing in the pasture looking at Jack's herd of sheep. Jack tells Mack how sheep make the best lovers because of there docile, sweet, and trusting nature. Furthermore, their body temperature is higher than a woman's so it makes for a particularly hot session.
Mack needs some further encouraging so after seeing what a great time can be had, as shown by Jacks repeated endeavors, he decides to give it a go (after all, their leave is almost over and he's getting a little desperate... OK a LOT desperate).
So Mack grabs a sheep and tries to give it a go. After a few minutes, Mack turns to Jack and says, "I don't know man, this just doesn't seem to be working for me."
Jack walks over and grabs the sheep buy the head and stares into it's face for a few minutes and replies, "Well no wonder, you picked the ugliest damn one!"