Yep, Once upon a time a scientist was sitting on a rather long plane flight across the Pacific. Next to him was an intelligent well mannered and dressed woman minding her own business.
The scientist broke the silence with "I have heard that long flights seem shorter if you talk with the person sitting next to you".
The woman put her book down and lowered her reading glasses "so tell me what is the difference between rabbit droppings and cow manure?"
"I have not a clue" came the reply.
"Well if you don't know your sheet we can't talk."
How's that for DD? Down & Dumbed