There are many Czech surnames motivated by parts of human or animal body. Some of them are connected with sexual or fecal activities. These surnames are pejorative and many of them were changed during the time and disappeared from our onymic system. This article is focused on surnames which are meant to be obscene only by a folk etymology but their real origin is different and they have nothing to do with vulgar common nouns. However, the pressure of the folk etymology is so strong that many people rather change their surname not to be objects of jokes and notes about their names.