I haven't had that done to me often, but once upon a time my then-girlfriend was standing behind me and slipped her hands into my front jeans pockets -- just being affectionate I guess; I don't think she was trying to pickpocket me -- and the acute tickling sensations that jolted through my body were electric. Immediately I emitted a desperate shriek of giggles and gripped her wrists, trying to pull her hands away. I heard her puff out a little delighted scoff of surprise -- "Does that tickle??" The answer was self-evident, of course, and needless to say her response to finding out that it did in fact tickle -- that the maneuver was delivering a red-alert, five-alarm, defcon 1 tickle emergency -- was NOT to withdraw her hands immediately out of a compassionate regard for my comfort and composure, but RATHER to leave her hands in my pockets and kind of wiggle her fingers back and forth. There wasn't a lot of room in there for her fingers to move -- all they could do was bend and straighten bend and straighten -- but that was more than enough; if simply having her hands in my pockets was debilitating, the addition of those subtle movements was thoroughly incapacitating.
The giggles were cascading out of me in a nonstop series of crescendos as I bent forward at the waist and tried to thrash back and forth, but having her weight at my back limited my movements. I staggered forward and to the side and to the other side but she clung to my back like a counterweight, laughing merrily in my ear, those infernal fingers of hers flexing all the while. This was of course in a public place -- a party at an acquaintance's house, specifically in the backyard -- so my frantic spectacle was on full display, and the increasing decibels of my helpless laughter reached a bemused audience.
By the time I finally freed myself from the nonstop torture -- I think I finally wound up dropping to one knee at the same time that I finally pried one of her hands out of its pocket -- my laughter had spiraled into a high-pitched undulation of squealing giggles, a sort of gaHAHAHA gaHAHAHA that conclusively obliterated any remaining sense of personal dignity I might have hoped to cling to. When I was finally freed, the laughter slowly subsiding and my cheeks blazing with exertion and embarrassment, everyone else went about their business; my girlfriend planted an affectionate series of playful kisses on my cheek and offered to go get me a drink.