XX - Onions and X-mas Tree

A family is at the dinner table. The son asks his father,

'Dad, how many
kinds of boobs are there?

The father, surprised, answers, 'Well, son, there are three
  kinds of boobs:
In her 20's, a woman's are like melons, round and firm.
In her 30's to 40's, they are like pears, still nice but
  hanging a bit.
After 50, they are like onions'.

'Onions?'

'Yes, you see them and they make you cry.'

This infuriated his wife and daughter so the daughter said,
'Mum, how many kinds of 'willies' are there?

The mother, surprised, smiles and answers, 'Well dear, a man
goes through three phases. In his 20's, his willy is like an oak tree,
mighty and hard.
In his 30's and 40's, it is like a birch, flexible but
reliable. After his
60's, it is like a Christmas Tree.'

'A Christmas tree?'

'Yes - the tree is dead and the balls are just for decoration.