From a review of Ascent of the A-word by Mark Judge, at the conservative acculturated site:

Let me lay out my theory for why the term asshole is derogatory. Doing so will explain why I think I can’t find much sense in Geoffrey Nunberg’s new book.  For me, calling someone an asshole is an insult for pretty obvious reasons. Human beings equate virtue and civilization with cleanliness…. To refer to someone as an asshole is to equate them with filth and disease, and thus to make them seem uncivilized and not virtuous. Its’s pretty simple: filth and bacteria equals decay and sloth. That’s my reading, based on common sense. Calling people these kinds of names hasn’t changed in human history, even in the digital age.

Well, that’s a theory, but it leaves you with several questions; for example, why don’t the Italians and French use their words for the anus as a term of abuse? And then it hits you: Well, of course — they have bidets!