Rectum

Little Johnny has been really excited during show and tell. Finally, the teacher calls on him. Johnny runs up to the front of the class and begins to excitedly tell his story. "Last night my dog got off the leash and he ran out in the road and a car ran over his ass!"

Teacher said, "Johnny, "ass" isn't a very nice word. You should say "rectum".

Johnny replied, "Rectum??!! Hell yes it rectum, it KILLED 'em!"