"Fishing With Dad" joke

One day, Little Johnny and his dad went to the river to do some fishing. Sitting on the bank, his dad lit up a cigarette. Johnny looked at him and asked, "Can I have one of those?"
"Well, Johnny, can you touch your asshole with your dick?" his father asked.
"No!" Johnny replied.
"Then you aren't old enough," his father said.
A little while later, his dad opened a beer. "Can I have one of those?" Johnny asked.
"Can you touch your asshole with your dick?" asked his father.
"No!" Johnny replied.
"Then you aren't old enough," said his father.
Later on, Johnny pulled a chocolate bar out of his jacket pocket and was about to eat it when his father asked, "Can I have some of that?"
"Well, dad, can you touch your asshole with your dick?" Johnny asked.
"I sure can!" replied his father.
"Good! Then go fuck yourself, cause this is mine!" replied Johnny.