In the vernacular, "wanking". Self-rape, to be more precise.

Ah yes, that old chestnut. Introducing oneself to the 5 lovely daughters of Mrs. Hand is the illicit discovery and secret pleasure of most boys well before they are introduced to anything more...bi-directional. But really, what's the big deal? Well, the very health and unity of society is at stake, said the Enlightenment rationalists. Yes indeed. It may surprise you to know that the horror and loathing associated with masturbation in our parents' and grandparents' days was driven not by churchmen, not even Victorian churchmen, but by humanist medical doctors. That's right. You heard it first here. In the so-called Enlightenment 'freedom' of men rejecting God's rule, we discovered the vicious control of genuine puritanical tyranny (and that without bounds): the avowed public control of private life, even to its most secret moments, by those who came to worship other gods.

But you can read more about it here. And may I recommend you do so, because it is not only fascinating, but funny. What is more, I shall be having more to say about it shortly. Make no mistake: it is not whether we will be ruled by gods, but which ones that is the vital question.

(thanks to matt for the link)

...and for the record (albeit in fine print): I don't think that masturbation is a Good Thing.