I think I have witnessed the most atrocious manifestation of the quintessential ehell sinner, some years ago.
One of my best friends happens to be the daughter of an important writer, very famous & bestselling in our country. (she doesn't especially want this fact to be known by people she meets, as it is a lot more important to be seen as who she is, rather than as Mr. "Famouswriter"'s daughter.)
Back when we were in high school, we participated into a national school competition; all the participants, from all across the country, were staying at a small hotel in the town where the competition was happenning and we tried our best to befriend each other.
So, there was this guy we gotten into some talk with, and we invited him over to our room to play cards. At one point, he notices my friend's name tag so he inquires: "Oh, are you related to *that* "Famouswriter?" She confirms and he proceeds to ask her about him- so she kind of ends up telling him the story of her family: she lives with her mother, who is divorced from Mr. "Famouswriter" and remarried, but she doesget along well with her father, his new wife and her little half-brother (the new wife's son), as well as with her step-sister (her step-father's daughter from a previous marriage).
So here's when this guy says: Geeee... they're hooking up like crazy, in your family! (actually he used a very ugly word I'm not sure even how to translate- something along the lines of "sl*t-ing around").
You can imagine how our jaws dropped in a fraction of a second, and all we could utter was "Get out! NOW!". May he burn in Etiquette Hell forever!