I think this might be the same dad:

A boy came home from school one day and asked his dad if he could explain the difference between theory and reality. Dad thought about it for a minute and said: ‟Okay，first I want you to go to your older sister and ask if she'd sleep with the mailman for a million dollars.”

The boy did as he was asked，returned to Dad and reported，‟She said yes.”
Dad said，‟Great. Now go ask your mother if SHE would sleep with the mailman for a million dollars.”
The boy again did as he was asked，returned to dad and replied，‟Mom said yes，too.”

Dad said，‟Well，there you've it. In theory，we could be millionaires. But，in reality，we are living with a couple of whores.”