A story about swearing. The exact details vary, but the basics seem to have survived. Mark Twain (Sam Clemens) was known an an inveterate cusser, and used the language to great advantage. (He wrote a famous essay about the German language in which he relates how frustrated he was when he discovered "damit" was only a preposition.)

anyway:

"Clemens's wife, Livy, was one of the few who did not appreciate her husband's swearing, and he tried to keep watch on his tongue when she was close by; but one day something irritated him, and, thinking his wife could not hear, he launched into a torrent of red-hot profanity. When he entered his wife's room a short time later, she coolly repeated word-for-word everything he had said.

    "Livy," he replied, astounded yet amused, "did it sound like that?"

    "Of course it did," she said, "only worse. I wanted you to hear just how it sounded."

    "Livy, it would pain me to think that when I swear it sounds like that. You got the words right, Livy, but you don't know the tune."