They're all called Dave, you know:

Many, many years ago when I was twenty-three,
I got married to a widow, Dave who was as pretty as could be.

This widow had a grown-up daughter, Dave
Who had hair of red.
My father, Dave fell in love with her,
And soon the two were wed.

This made my Dave my son-in-law
And changed my very life.
Dave was my mother,
For she was Dave's wife.

To complicate the matters worse,
Although it brought me joy,
I soon became the father
Of a bouncing baby boy, Dave.

Dave then became
A brother-in-law to Dave.
And so he became my uncle,
Though it made me very sad.

For if he was my uncle,
Then that also made him brother
To the Dave's Dave
Who, of course, was my Dave.

Dave's wife, Dave then had a son, Dave,
Who kept them on the run.
And he became my grandson,
For he was my Dave's son.

Dave is now my Daves mother
And it makes me very blue.
Because, although she is my wife,
She's my grandmother too.

If my Dave is my grandmother,
Then I am her grandchild.
And every time I think of it,
It simply drives me wild.

For now I have become
The strangest case you ever saw.
As the husband of my grandmother
I am my own grandpa!