I guess it's not so much that people are getting their rocks off to it that makes somthing porn. What I believe makes something porn is that it is being produced with the intent to be sold because of it's sexually provocative nature.
Tickling videos fit this description - I mean, producers primarily make them to sell them to people who find tickling sexy. People who are probably going to masturbate to said video.
In that sense, then, tickling videos are porn.
Artoos comments line up pretty well with the dictionary definition of porn, but I myself can't buy into this definition for a couple of reasons.
1) I don't believe that something <del>should</del> can be defined by the intent of it's creator. We define things by what is actually there, not what somebody wants it to be. Hence, porn should be determined by content.
Consider the phrase, "soft porn." By the dictionary definition, soft porn would be material that the creator only has mild aspirations for sexual gratification, while "hardcore porn" would refer to material to which the creators really really want us to spank our monkeys. This is based on the criterea for porn being based on <em>in</em>tent rather than <em>con</em>tent.
But that's not the reality. The reality is we classify soft porn vs hardcore by the content. If it's sexy women posing in see-through lingerie, it's soft porn. If it's group anal sex we're talking about, then we tend to label it as hardcore.
2) Does it make sense that producers of porn have any other intent than to make bucks?
Hypothetical: What if producers of porn suddenly found out that people were buying their product in droves for reasons other than sexual gratification? Say, to read the jokes or to study a healthy body for medical purposes?
Do you believe the porn producers would take any offense, or try to put a stop to it? After all, these customers are not fulfulling the <em>intent</em> of the producers.
Hypothetical: Pedophile Pedro works for a firm that markets children's clothing. Pedro is responsible for producing the catalogues. He takes great satisfaction in including pictures of all the children especially in the undergarment section. He wants to please his online pedo pals.
By the official definition of porn, since it's Pete's <em>intent</em> for this catalogue to give sexual gratification, anybody who shops with it is looking at "pornography." The reality is that most people are simply shopping for clothes for their children, and if you suggested they were holding pornography in their hands, they'd probably take a few steps back away from you.
In summary, the dictionary definition of porn needs an overhaul. The criterea should be determined by content, not intent. So to answer the original question posed, I would say that tickling videos are not porn unless their content also includes recognizable elements of pornography. Nudity, physical contact with genetalia, etc.
Fully clothed models tickling each other does not qualify as porn by any reasonable definition.
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