Angle makes a difference. If I just tickle my feet by approaching from the bottom like I would somebody else, it just feels sort of nice. But if I go over the top - so, imagine sitting on the ground with your legs directly ahead of you, then reach out with your hands so your fingers curl over your toes - and then slide your nails down your feet. It won't make you laugh out loud, but it definitely makes you squirmy and tickly.
Also some showers are unbearably ticklish on me. Depending on how hard they are spraying down - lighter ones will tickle under my arms, heavier ones will tickle my feet if I hold them bottom-up while washing. Most showers don't really, it's just certain water pressures that are really tickly.
And my underarms are bad enough that I can tickle myself there with any sort of thing like a blade of grass and it will be ticklish enough that I have to pull my own hand away. :lol: