Oh yea, the other day I saw a rule 34 of Luke Triton and Ness. STOP. Luke Triton and Ness is a pairing most haven't thought of, and I have yet to see a rule 34 of it, so for the time being, this is an exception. If you do happen to see or make one, contact me at email@example.com :)
(Rule 34's brother in childhood smashing is rule 64 )
Additionally it is accepted that the rule itself has limitations and you cannot be too specific on the content of the item in question.
Most commonly used on various message boards for various reasons, from humor to cruelty.