First off, let me welcome you to the TMF! Good bunch of people here. Hope you make friends, and have fun!
That was easy. Your question, however...
I'd stay away from the word "Fetish", as it freaks people. "I like to tickle" will go over much better than "I have a tickle fetish."
Also, are you planning to tell someone? When I told my folks, they figured, as long as I wasn't tickle attacking women on the street, it wasn't anything to worry about.
Friends? Harder. A friend of mine came across my very first video, and asked me about it. After fumbling out that tickling was a favorite passtime of mine, he commented "Really? That's very interesting." He asked some more about it, seeming truly facinated. Anyway, we're still friends.
I think, like most of us do, or did, that if you do tell anyone, they'll go screaming off into the night, and a few will (Figureatively), but I think you'll be surprised how many are O.K. with it, and some may even find it endearing.
All in all, try and gauge the reactions of people you plan to reveal this to, as everyone is different, and do it gradually. Maybe you and some friends will see a movie, or T.V. show with some tickling in it, say that you found it a little surprising, and ask what they thought. This way, you may get a better idea who you want to tell.
In any case, welcome again, and good luck!