Here are some gems from the delightfully wry brain of an etiquette hero, and our takes on their modern translations.  Then: "A gentleman never discusses his family affairs either in public or with acquaintances, nor does he speak more than casually about his wife. A man is a cad who tells anyone, no matter who, what his wife told him in confidence, or describes what she looks like in her bedroom. To impart details of her beauty is scarcely better than to publish her blemishes; to do either is unspeakable."  Now: Emily could have been speaking directly to Mark Zuckerberg here, moments before he began that really mean blog post tearing apart the chick from "The Girl With the Dragon Tattoo." The audience to such flagrant meanness was once a bro's smoking buddies; now it's anyone with an Internet connection and the ability to Google.  Taking to one's social-media channels to speak ill of a co-worker, friend or lover remains, well, unspeakable. Vent your frustrations with old-fashioned gossip or scrawl criticism in a diary or in a personal e-mail instead of hitting "publish."  Then: "The letter you write, whether you realize it or not, is always a mirror which reflects your appearance, taste and character. A 'sloppy' letter with the writing all pouring into one corner of the page, badly worded, badly spelled, and with unmatched paper and envelope -- even possibly a blot -- proclaims the sort of person who would have unkempt hair, unclean linen and broken shoe laces; just as a neat, precise, evenly written note portrays a person of like characteristics.
Shilling etiquette advice is an old and illustrious profession. As long as there's been a society, there's also been appropriate social behavior (and a goodly number of schmucks who do everything...