In my (few and far between) personal experiences, genital tickling is a double-edged sword. I can't really provide a reliable opinion, of course, since I lack a clitoris (curse this body and it's limited range of erogenous zones!), but from what I've seen and felt and heard, the clitoris traverses a vast range of sensitivity. It's easy to over-stimulate, and then the feeling changes from tickling, however gaonizing, to a quality that can be described as painful. I know the watered-down version of this traverse from my own naughty bits, and it really is something that can turn a great experience sour. Aside from that, the choice of tickling instruments is elemental. I've found that feathers (I normally abhor them) are quite effective in this region. If I try something as kinky as this, I normally progress like this:
First, I ask my partner is she's down with it. Nothing can put a smackdown on her pleasure like an overzealous guy suddenly invading her privacy in unwanted ways. Then, if she agrees, we start by making out and building tension. I don't tickle her a lot during this time, since sexual tickling needs to be, in my opinion anyway, more pleasurable than torturous. Once we're both good and ready, I get down for the action, with carefull and gentle strokes with a soft feathertip. It's important to be very, very careful. Unexpected jerks of her hips or my hands could cause the feather to jab her or apply too much pressure, which would probably hurt like the dickens - I don't know, I always hold the feather just firmly enough to direct it, but loosely enough so it can break away when undue pressure is applied, so that never happened to me. During the tickling, I keep one eye on what I'm doing, and the other on her reaction. When it looks like she's starting to slip (hard to describe), I stop. Until now, I've only had positive feedback, aside from one scolding where I stopped too early (whoa, she was so pissed... 'I GOT SO CLOSE, YOU BASTARD!!!'), but still - better safe then sorry 😉
But, as I said, I don't do it that often. I much prefer giving head... *snicker* Oh, and ruthless tickling. Definitely ruthless tickling. Nice topic, though!