I used to be ticklish as it happens, and I used to flail about dangerously, so my uncle tied me up, I tried to fight him off but I was only 8, the whole family thought it was hilarious to see me trussed up and tickled for close to an hour.
Ella, remind me... if I'm ever invited to one of your family reunions, remind me to stay the hell away. And you should stay away too. But I guess your family is really fodder for another thread... Sorry.
I have noticed that the real hotspots of ticklishness tend to be at the points where tendons attach to bones. That's why a quick thumb-and-finger pinch on the thigh just above the kneecap can drive someone through the roof. Also, it explains why ribs are so ticklish... they're practically woven into a cage of interstitial muscle and connective tissue.
The ends of the collar bones are great spots for a deep tickle, as are the hipbones.