When I was 4 or 5 yo, my parents took me to their friend's house. They had cute daughter, age like mine. When we were alone, I asked her to tickle her feet and she agreed. We were behind sofa, and she took off her sox. She wasn't ticklish, but I continued to play (I was too young to enjoy it like today). But... When I turned back, I saw her elder sister watching us with smile on her face! I run away out of the room, ashamed. Later, she told EVERYONE what we did, and she found it cute. Also, our parrents teased me with telling: "Don't worry, we will arrange wedding next Sunday 😉" and laugh watching me blush.
A lot years later, I met beautifull blonde. During chat I run my finger once trough the gap between her soles and sandals. She almost screamed. 😀 So I made a plan...
Few weeks later, she came to my house. I bought her beautifull black pantyhose, and asked her to try them to. So, she went to the bathroom, put them on and when she came back... After few (true) compliments I've kissed her and told her to sit on the bed. Then I took her both legs and place them on my lap and slowly tickled her feet. Nothing. I tried a few different types of tickling but nothing happend. Not even a slight move. She was ticklish only when someone suprises her, and even then she would only say "Stop it!" (no laugh, no move). When she is concentrated (and/or expecting tickling) then her ticklishness is - zero. :-(
At least, I told her about my fetish so she agreed to let me "tickle" her feet sometimes...