I can only remember a couple of episodes in which Olive Oyl gets tickled, not to say there aren't more. One of them had her suspended by one foot from a steel girder of a skyscraper under construction. Just as in Bootman's post, Bluto peels back the sole of her shoe exposing her bare foot which he commences to tickle. In order to avoid plummeting to her death (boy, talk about violence) she must resist the urge to move her foot too much but still has to laugh because of Bluto's wiggling fingers.
My particular favorite that would send the butterflies flying in my stomach whenever I saw that it was coming on was one called "Ghost Ship". I can't remember how old I was. I was just a young kid but old enough to get "aroused". Even back then I had a thing for foot tickling. But I digress. In this praticular episode, Olive, Wimpy and Popeye are at sea and come across a three masted ship with tattered sails and looking as though it's seen better days. After boarding the ship and looking around, one of the three, probably Popeye (memory gets a little fuzzy here 'cause I was starting to concentrate on what I knew was coming) says something to the effect there ain't no such things as ghosts. That's when a gagle of ghosts appears and says "Oh yeah?" followed by a whirlwind attack of the three protaganists. Popeye is next seen suspended by a rope around his waist high in the masts swinging back and forth with the rolling of the sea hitting first his head then his butt on the masts between which he is suspended. Wimpy is chained like a dog with collar around his neck. Before him is a table with a platter piled high with hamburgers. As he moves toward the table to get a burger, it comes to life and moves away out of his reach. He of course chases it only to reach the end of the chain and be jerked back like a chained dog chasing a cat. The table then walks closer again and this is repeated over and over again. Poor Wimpy can't figure out that he ain't gonna get a burger. Of course the best part is Olive's fate. I can remember my heart beating fast as the scene went to her. She's seated on the deck with her hands tied to a some part of the ship and her legs spread, ankles tied to cleats, big bare feet exposed. One of the ghosts then drips milk or cream onto her feet and then allows several kittens to start licking her soles whereupon she starts to laugh. Man, I loved that cartoon even though Olive has to have some of the ugliest feet around. But back then that didn't matter. After that scene, I would have to suddenly go to the bathroom or basement.
I obviously had the foot tickling jones before I saw that cartoon. I don't know the origins of that obsession. But that was my first visualization (other than my mind's eye) of a helpless woman who's bound and tickled on the soles of her feet.