A boy and his grandfather are fishing

The grandfather pulls out a flask and takes a swig. His grandson asks "Can I have a sip?"
"Can your dick touch your asshole?" replies the old man.
"No" says the boy.
"Then you're too young for whiskey"
A little while passes and the grandfather pulls out a cigarette and lights up.
"Can I try one?" the boy asks.
"Can your dick touch your asshole?" the grandfather asks again.
"No" the boy says
"Then you're too young for tobacco"
Dejected the little boy reaches into his pocket and pulls out a bag of M&Ms to snack on. The grandfather notices and says "Can I have some?"
"Can your dick touch your asshole?" the boy asks
"Yes" the old man says smiling
The little boy smiles back and says "Then go fuck yourself because you're not getting any of my M&Ms"