Ermordenung
Ermordenungs are a monstrous humanoid native to domain of Borca in the Ravenloft setting for Dungeons & Dragons. Originally normal humans, they have been subjected to alchemical alterations invented by the Darklord of Borca, imbuing their entire bodies with lethal toxins as well as supernatural beauty. This makes them natural assassins, since a touch or a kiss can easily kill a person. This being a Gothic Horror transformation, there's a sting in the tail; ermordenungs both incapable of turning off their poisonous touch and breath, and are immune to all poisons... except their own. So to become an ermordenung means to be completely cut off from all physical intimacies, because even another ermordenung will die if you have sex with them (of course, in that latter case, you'll die too). Well, technically there's ways around this, but since that means shacking up with a Flesh Golem, a Vampire or an undead lover... yeah, not exactly a "free lunch", is it?