The Mechanics and Rhetoric of Conversation : Page 42
This distinction is very important. When J. Edgar Hoover called certain gangsters rats, he was not indulging in slang but in figurative truthtelling. Calling one's mother-in-law a flat-iron or a teacher a battle-ax is slang because doing so is
not fair, is not telling the truth about them, is really slandering them, for they are both, viewed in perspective, rather fine persons, or at least not nearly as bad as the picturesque comparisons imply. One can almost say that a gentleman or lady who follows Newman's requirements of never willingly giving offense is not likely to become guilty of slang. Just as one would not call a cripple a crutch-hound, so one should not call sickly or homely or fat or mentally retarded or crazy persons such names as wheezepill, toadface, blimp-belly, featherhead, or screwball. Since such people are not responsible for their shortcomings, it is uncharitable to apply derogatory comparisons to them. To do so is to be slangy, slangy in the correct sense of the word.