A young woman asks her mother, "Mom, how many kinds of penises are there?"

The mother, surprised, answers, "Well, daughter, a man's penis goes through three phases ..

In a man's twenties, a man's penis is like an oak, mighty and hard. In his thirties and forties, it is like a birch,flexible but reliable. After his fifties, it is like a Christmas tree."

"A Christmas tree?"

"Yes, dried up and the balls are there for decoration only."