My best friend is a lawyer as well as a former abused wife. Her ex-H was also a convicted rapist and she now believes he was molesting his daughter, as a very young child. probably also his son at a later age.
My friend reports that her ex used to tickle his daughter (and other little girls) unmercifully. She has since found that there can be a link between this and sexual abuse. Not that all tickling is connected to sexual abuse, but it is part of the salami tactics that abusers can use.
Sexual abuse is not primarily about sex, it is about control and manipulation. When you are being tickled, the natural response is to laugh, even if you hate being tickled. We cry, "No, stop, please stop!" while laughing, and an abuser can use this to mentally justify that despite the "No, please stop!" cry, that because the victim is laughing, they are actually enjoying it despite their verbal protests. it also "allows" the abuser to blur the lines of consent - "I thought she liked it." So an abuser instigating a tickle game and then keeping on going with it after the victim has made it clear, they don't want it - very definitely, huge warning signs.
If the tickler is someone younger, it is possible that they really don't get that the victim really doesn't want it, and the laughter is no indication at all of consent or complicity. Sometimes you can talk the tickler through this and make it clear - do not do this, because the neurological response is to laugh, this does not imply consent or enjoyment in any way. But if this really fails - I don't like this, but you can try subjecting the abuser to extreme non-stop tickling and point out, "I thought you were enjoying it because you were laughing." Make it clear, by demonstration on them, that being tickled until you are throwing up is not enjoyable despite the laughter.
I used to tickle a good friend of ours. I really tortured him - not by direct tickling, but by finding ways to play with the idea of tickling. He was extremely ticklish! I would sometimes, while sitting on the other side of the room, make ticking motions with my hands and say, "I'm tickling you from over here," and it would set him off. And once I actually stood behind him with my index fingers touching his ribs, not moving, not tickling, just leaving my fingers there. I have since had it done to me - even thought you're not being tickled, it is too close for comfort and is agonisingly effective.
I also was very ticklish, especially my feet. I actually learned to over-ride the impulse to pull my feet away - if someone began to tickle my feet, I would mentally tell myself, "This person is pressing hard on my feet and hurting me." I mentally re-wrote what was happening and over-rode the tickle response. Or you can tell yourself, "That is me touching my own feet," (or ribs). It is physically impossible to tickle yourself, so find a way to trick yourself into thinking you are touching yourself, and it is not someone else. Press your own fingertips into your sides, or some other part of your body so your fingertips have a sensory input that could match the feel of you touching your own body in a tickle zone. Then keep telling yourself, "This is me doing it." And if you are able to not react to a tickler, they soon stop ever trying it on with you.
You an use this to help someone de-sensitise themselves form tickling. If you 'tickle' the student on the edge of a tickle zone or away from a tickle zone and tell the person, "Keep telling yourself that you are not ticklish or that you are the one doing the touching," you can build up resistance to tickling. But the 'victim' in training needs to always have control, needs a code word to make you stop. They need to know you will stop, instantly. It can make a huge difference, once you successfully desensitise.
But if you have a group of people anywhere, and someone is a torturing tickler, you need to make it stop. It is abuse to impose a physical contact on any person without their consent. And laughter does not imply consent or enjoyment. I would also keep a very close eye on the tickler for other signs of them being a potential abuser.
Marg