The Mechanics and Rhetoric of Conversation : Page 41

Expletives bring to mind the use of slang. If I gauge sentiment correctly, people who brazenly boom a profanity, turn pale if anyone hints that they have been guilty of slang. Perhaps the surest way to ease one's mind about slang is to realize, first, that any sort of profanity or quasi profanity is worse than slang, artistically as well as morally, and, secondly, that anything else which isn't offensive to one's mother is nothing to worry about. Technically speaking, slang is the comparing of a good or indifferent thing to something ugly or unpleasant or bad. Calling a girl, whom God gave little sparkle but the character not to drink or "pet," a flat tire is slang. Similarly, calling a student upon whom God bestowed a slow, if perhaps willing, mind a dumbbell is slang. But calling an unnecessarily stubborn fellow a mule is not really slang.