An evil form of tickle torture would be ..

Tickling in some spots is sexy and arousing, and in other spots it's just very, very, very irritating. Nose or ears are the latter as far as I'm concerned.

Somewhere in Solzhenitsyn's "Gulag Archipelago" there is a section listing the kinds of torments visited by interrogators on inmates of Soviet prison camps, and when I looked at this book as a teenager I was initially excited to spot the heading "Tickling" in the list. When I read on, the solitary example given was the practice of poking a feather up the nostril of the victim. Nasty. But disappointing. Not what I call tickling.

If I'm spread eagle, lightly grazing the palms of my hands and tracing your fingers up and down the inner side of my arms will drive me insane. It tickles but feels good at the same time. Friggin' ridiculous.

Also, clit tickling with a small paintbrush sounds insane. Especially if one is tied tightly and can't squirm around to lessen the sensation. Might be curious to try that some time.

Clit tickling with a powderpuff will drive a grown woman to tears; they don't clump due to wetness, and are more gentle and less irritating over long periods compared to most paintbrushes. The perfect interrogation tool, honestly!

An evil form for me would be holding the ticklee in place in a embarrassing and humiliating way. Or tie them in a way were there are armpits are exposed, but they cant close there arms fully to "protect" them.