这个笑话的原版我找到了,
The manager of a shop was scolding one of his staff.
“I saw you arguing with a customer,” he said, “Will you please remember that in my shop the customer is always right. Do you understand?”
“Yes, sir,” said the shop assistant. “Customers are always right.”
“Now what were you arguing about?”
“Well, sir. He said you were an idiot.”