a good wank
 

A young boy of about fourteen and his father are avid woodsmen. One day, on a trip to the country, dusk catches them in the woods. They set up their tent and, after dinner, they go to sleep. The man wakes up in the middle of the night and says to his son, "What are you doing, son?"
After a short silence he answers, "I'm wanking, father."
"Oh. And how is it going?" he asks.
Another minute of awkward silence passes.
"It is hard, but I can't really feel anything," says the boy.
To which his father replies, "You should maybe try it with your own ****, then."

good one