Just saw this thread and decided to bring it to life.
When I was a college sophomore, I had an on-off relationship with a young lady about a year older than myself whom I'll call Diane (not her real name).
We sparked at times, and at one point right around Halloween, I was at her place and we were messing around a bit. I used the restroom and when I came back, I saw she was lying on her stomach, reading a book on the pillow on her bed.
She was wearing these blue slippers, I remember that very well. In any case, she was absorbed and I had the chance to sneak up on her. I pounced, and actually got her legs trapped under me, her feet sticking out.
I whipped Diane's slippers off and scratched at her feet a bit. She giggled and squealed like she always did when I tickled her, but feeling bold (and with a couple hits of Jack Daniels in me) I shifted around and started licking her sole.
It was the only time I ever heard her go berzerk. Diane burst into hysterics, turning red (I saw after I stopped) and pounding the bed. I stopped, feeling insecure about it, but she never said stop. She twisted away and said something about not letting me do that again, but she wasn't upset or angry at all.
We started drifing apart not long afterwards (the on-off thing got to be too much), but I always wondered afterwards how far I could have pressed that day.