When I was in high school I used to tickle my friend's sister every chance I got. It was maddening for me because every time I went over his house I would have this strong urge to go get her, but I always had to be patient and wait until I could get some alone time. It was always fun because we'd start off goofing around, then next thing I'm taking her long soccer socks and tying her wrists and legs. She never seemed to mind and never though anything about the tickling. I would always tickle her feet and stomach while she rolled around trying to free her hands. She was 2 years younger than me and I always felt somewhat embarassed as she could feel my erection through my pants as I was leaning against her tying her hands behind her back. She likes to still tease me about tying her up even after it's been like a decade. Something tells me I gave her a little bit of a kinky side.