[craigster59]

My favorite has always been the difference between theory and reality:

A young boy went to his father and asked, "Dad, what's the difference
between theory and reality?"

"Well, son, the best way to explain this is a practical exercise. Go ask
your Mom if she'd sleep with a stranger a million dollars and come tell me
her answer."

The boy returned and said, " She said she would, Dad." "OK," replied the
father, "Go ask your sister the same question."

The boy returned and said that his sister also answered yes to the
question and then asked his Dad, "What's this got to do with theory and
reality?"

"It's simple, son. In theory, we live with millionaires.
In reality, we live with a couple of sluts."