"Rule 34" is a rule on the internet, that states that there exists porn of everything. I had originally taken the rule to refer specifically to fan fiction, and the transformation of every imaginable television program, movie, comic book, or other entertainment medium into pornographic drawings and stories. But the rule could, I suppose, exist for acts or preferences.
And Rule 34 is not true. I know that here I am assailing one of the pillars of the internet, but I will explain why Rule 34 is not true.
To do this, we have to know some basic theory about the number line. The number line, which stretches from negative infinity to positive infinity, has an infinite amount of positive integers, and also an infinite amount of negative integers. Although these numbers are infinite, they are infinitely outnumbered by the even more infinitely large set of rational numbers. And those are infinitely outnumbered by the irrational numbers.
Rule 34 might be true if you think of it in terms of talking about integer infinities. But does it apply to the other infinities? While every "simple" fetish may exist, remember that every fetish can be compounded, which is the equivalent to our "rational numbers". I am sure hot air balloon porn exists. I am sure porn exists where people are eating salads. Perhaps these two even exist together. But even within the confined space of a hot air balloon, there are so many possible activities to be done that the combinations of them quickly approaches a very large number. The same applies to the issue of pornography based on fan fiction. There were seven members of the cast of Gilligan's Island. I am sure that Gilligan's Island pornography exists, but does every combination of it exist? Seven factorial is 5,400: even at the level of drabble, I doubt that every combination in which the seven characters of Gilligan's Island could find erotic release with each other has been described. And that is only one show. So even in the realm of these "rational" fantasies, it seems unlikely that everything exists.
But to continue with our metaphor, what about the irrational fantasies? An irrational number is a number that can not be expressed as the division of two other numbers. What about all of people's fantasies, that seem to be in a constant state of searching, yet not to find? What about the person fapping desperately, looking at different images of people on hot air balloons with different implements, that can not seem to conjure up what hidden, subtle formlessness their lust takes. Rule 34 can not apply to the pornography that lurks at the corner of people's imaginations, unknowable and unfulfillable.