"What are you doing?", asked the grandad. "You're 18 years old and wasting your life. When I was 18 I went to Paris, I went to the Moulin Rouge, drank all night, had my way with the dancers, pissed on the barman and left without paying. Now that is how to have a good time."
A week later, the grandfather comes to visit again. He finds the boy still in his room, but with a broken arm in plaster, 2 black eyes and missing all his front teeth.
"What happened?", he asked. "Oh Grandfather!", replied the boy. "I did what you did. I went to Paris, went to the Moulin Rouge, drank all night, had my way with the dancers, pissed all over the barman, and he beat the crap out of me!"
"Oh dear!", replied the grandad. "Who did you go with?"
"Just some friends, why? Who did you go with?"
"Oh!" replied the grandad. "The Third Panzer Division."