This question caught my eye since I've often been on the receiving end in these situations (a friend says "Hey, he's ticklish," or "Help me tickle him," and suddenly she's joined by one or more other friends, and helplessness ensues... which raises the question, Why does every woman in the world interpret "He's ticklish" to mean "He must be tickled now?" And why does every woman in the world respond so much more enthusiastically to "Help me tickle him" than to "Help me change this tire...?" But I digress.
I think there is a diminished-returns phenomenon at work in gang tickling. That is: two ticklers might make me more hysterical than one, but four aren't likely to make me more hysterical than two.
I've had the experience, actually, of being tickled by one person--laughing, struggling, trying to fend her off--and dissolving into helpless shrieking giggles only after another person joins her. Part of this is tactical: I can try to rebuff one pair of hands but am hopelessly outnumbered by two and thus surrender to my laughter. But I think the sensation of being tickled by two people is also often qualitatively more overwhelming than being tickled by one.
But if two people have reduced me to hysterics and are tickling me as I writhe on the floor, the addition of a third won't heighten my hysteria, if only because it can go only so high. If Jen and Amy are already tickling my sides and stomach and then Sarah joins in by seizing my knees, it changes the details of the experience--I'm aware that someone's begun tickling my knees, and yes ohmygoditdoestickle--but not the intensity of it.
Indeed, if one tickler has already succeeded in reducing me to frenzied begging and squirming by the time a second one joins her, I'm not sure the second tickler much affects the intensity of the experience. What she's doing to me does tickle and my nerve endings will quiver ignominiously beneath her wicked touch, but the intolerable nature of the experience is already cranked up to 11, if you will. There is no 12.
If anything, the main variable that gang tickling introduces into the equation is this: if one of your tormentors decides to stop, there will be no relief for you because the others are still contributing to your frantic helplessness.
