Since real experiences also count, I'll give mine. Since I had no siblings, I always enjoyed playing with my babysitter (who for now I'm just going to refer to as Alex) at every opportunity. She was fairly tall, had short brown hair and a very cheerful nature. Anyways, I really liked Batman as a kid, so I'd sometimes pretend to be him, while Alex would be Harley Quinn. One day, Alex had bought some candy before coming over and hid it as part of the game. After a fun chase around the house, I asked her where the candy was, but her lips were sealed. After remembering that one episode of Arthur where DW's imaginary friend is chained up and tickle tortured, I got an idea. I convinced Alex to let me wrap her up with my blanket, where I then tugged off her socks and started scribbling her soles. She started giggling like crazy, but didn't reveal where the candy was until after a few minutes. The way she laughed, her wiggly toes, and her soft soles did something to my brain that day. Whenever we played Batman together, I would always use tickle torture to get "Harley" to confess, and she clearly enjoyed it herself, considering how she playfully cried "Oh no, don't tickle my feet!" at least once. Once I grew up and learned what fetishes were, I finally realized why I enjoyed tickling Alex so much.