Lol Time to grab my abnormal psychology textbook definition...
...Wow. Whoever calls it a "disorder" has no idea what they are missing! This textbook I thought was pretty offensive about a lot of topics....
There is a movement to remove paraphilias, fetishes and other widely accepted sexual abnormalities from the "disorder" definitions. Or at least to abridge them to recognize the fact that these "abnormalities" are not disorders until they interrupt the normal functioning of an individual.
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"Fetish" is a word that has become commonly used to define a lesser degree of attraction to an act/object than it clinically is defined as. And it has come to be commonly accepted in that function as well. I write regarding sexuality and have come across the arguements time and time again. Bottom line, words, when they come into common and frequent use for other things will take on that definition as well. Take the word "cool" for example. Similar discussions would have taken place in that era as well regarding the slang definition of it as well.
Yes, clinically, tickling is not a fetish, it is a paraphilia. A paraphilia, in its loose definition, is something that creates sexual arousal or attraction in a person. A fetish, in its loose definition, is an object/an objectification that is needed to sustain sexual arousal.
In the common, slang if you will, usage of fetish, I believe tickling would be considered a fetish if it is something that arouses you. It is a passion if you spend time thinking about it, looking at related materials or talking about it, whether or not it arouses you. It is an obsession if you find it taking a large amount of your time (and it does not relate to your work or studies). It is unhealthy when it starts to keep you from functioning fully in society.
I would say that for us here on the forum it is at least a passion. I know that the reason many of us, myself included, are here is because we crave to interact with others who understand what we enjoy. As humans, we crave to surround ourselves with those who are like us. Hence forums like this one.
Thats my two cents and then some...