I've had a few experiences.
I'm pretty ticklish, and so when some people find this out the enjoy finding out where I'm ticklish, and how ticklish I am haha.
One time, I met this girl at a hangout thing with a few friends, and I was laying down watching tv with my arms behind my head on my own. Eventually she saw me and came up and laid down next to me to talk and watch the tv. She decided to find out if I was ticklish, and rolled over spontaneously and started tickling under my arms, which of course made me squirm and laugh. She only tried it for a second though to see the reaction it gave me. Then another girl came over and the first one pinned me down, and told the other one to take my socks off, and they both started tickling my feet and stomach and under my arms, but only for 30 seconds or something. It was fun though =]
A few weeks ago I was at another hangout, and I was wearing a ripped tshirt and shorts, and I had my feet up on a long chair, and I noticed this girl who is a friend of mine snuck a look at my feet. So I was expecting her to tickle me possibly. Then surprisingly another girl came over and lifted my legs up in the air and rolled me onto my back and put my bare feet in a lock and started tickling the crap out of them!
Then recently I was laying on my bed with my girlfriend, and she sometimes lifts up my shirt and starts tickling my stomach and sides and under my arms when we're laying on a bed, and so I'm laying there giggling and enjoying it, and I had my feet underneath the bar at the end of my bed, because it's more comfortable to have them under the bar than resting on the bar, and she realised my feet were trapped, so she jumped down to the end of the bed and started tickling them a lot for a few minutes, and I couldn't move them at all. She loved this because I have very ticklish feet, and it made me laugh a lot =]
there are other stories, but here are 3.