Funny this should come up as I was just remembering the exact instant I internally realized just how much it was a part of me. The interest as an activity goes back to before I can remember, and carried through childhood as I was always tickling cousins, friends, and girls I would hang out with.. but the one instance that cinched it all together for me occurred in 8th grade.
It was gym day and the school's rules were that anybody who was unprepared for gym (as in didn't have gym clothes or sneakers) could not participate in the day's activities. That day softball was on the agenda, and there was a group of about 8 of us who had been told by the gym teacher that we were not playing and had to go sit on the sidewalk next to the gym doors of the school. It was late Spring and that was a shady spot, so it was comfortable.
The rest of the class headed over to the field. We were left mostly unsupervised to converse and horse around or do our classwork or whatever it was to occupy our time. One of my friends, Fred, was the guy who rarely participated in gym class so it was no surprise that he was among us. For me it happened once in a while. The surprise was the 2 fairly popular girls that were there. One girl, a girl I already had a minor crush on, was forbidden from playing because she was wearing sandals that day.
Her name was Brooke and her friend's name was Jaime. Brooke had slipped off her sandals and began to walk around in the grass barefoot, before deciding to sit on the sidewalk, cross-legged, just a few feet from me. Jaime was still walking around aimlessly, come to think of it she was prepared for gym and wearing sneakers but decided to be a good friend and stay out with Brooke (we were all pretty bored) but we all were conversing about whatever nonetheless.
Then, Brooke lies down on her back and straightens her legs out, feet pointed toward Fred and me.
I was not doing anything to make it obvious that I was noticing this and continued my conversation with Fred. Jaime, for some odd reason, decides to go over and sit on her friend Brooke, and she stayed there. Brooke didn't complain either. And the next thing I see is Fred reach over behind him and pick a blade of grass and proceed to drag it lazily along the bottom of Brooke's foot. Jaime asked her why she was laughing, to which she responds "Something's tickling my foot!" Fred continues, Jaime begins to smile and sort of tease her about how ticklish she is, saying something like "Brookie, it's only a piece of grass!" This tickling kept up for what seemed like minutes. I was paralyzed watching all of this unfold before my widened eyes. I couldn't believe it.
The girl's laughter was so musical and sweet and feminine, and she had such cute, tan feet with pink soles too, I was simply amazed. She protested very little, just kept laughing, only saying something like "I can't move!" and "It tickles! It tickles too much!" It was 1993 so the memory is a little fuzzy, but I'm pretty certain that at one point she was begging through her laughter "Please, my feet are too ticklish!" Keep in mind I already had a crush on her, well that went full-blown after this episode. I also discovered at that time that I had a sexual attraction to tickling that was involuntary. Luckily for me there was plenty of time for that situation to calm itself down before I actually had to get up and walk. I was lost in my own world for the next 2 weeks or so and my life was never the same since from that moment forward.