There was a really tough drill instructor in the Marine Corps. He believed that all Marines should be as tough as he was. So one day he called aside four new recruits and told them to get undressed and stand in a line. As soon as they had done so, he took a stick and belted the first recruit in the stomach.
"Did that hurt?" barked the drill instructor.
"No, sir!!" snapped back the first recruit.
"Why not?" said the drill instructor.
"Because I'm tough, and I want to be a Marine."

Pleased, the drill instructor turned to the second recruit in line. He hit him in the face with his stick, so hard that the man's jaw nearly broke.
"Did that hurt?" barked the drill instructor.
"No, sir!!" snapped back the second recruit.
"Why not?" said the drill instructor.
"Because I'm tough, and I want to be a Marine."

The drill instructor turned to the third recruit, ready to go through the same process. The third recruit had a large erection, so the drill instructor took his stick and struck the erect penis.
"Did that hurt?" barked the drill instructor.
"No, sir!!" snapped back the second recruit.
"Why not?" said the drill instructor.
"Because it belongs to the guy behind me!"