This is actually a harder question than it appears at first. I've been fortunate enough to have fulfilled many of the things I wanted to do, and have been blessed with the companionship of some very adventurous women in my life so far. Through creative role-palying, I've been able to explore interrogation fantiasies, kidnap scenarios, creative costuming and one particularly interesting evening that started out as a "drug-deal-gone-bad" scene and ended up as a sexual marathon that I don't even know if i have the proper words for.
However, there is a fantasy I could share with you. Keep in mind that this is a fantasy, and I have no mysogynistic tendencies. (Who knows, perhaps I'll meet some nice young lady on the TMF who'd like to role-play it someday....)
The most important part of this fantasy is the bondage itself. She is on her knees on a low platform or table. Her feet hang over the edge with straps fastening her ankles to the platform, and additional straps over her upper calves. There is a padded, horizontal bar suspended from the ceiling by a crank-chain. Her arms are above her head with her elbows bent over the suspended bar. With her hands now pointed downward, her wrists are fastened with thick straps and her elbows are cinched together as much as they can be brought together. The crank-chain pulls the bar up as high as it can go. A bit of ropework runs from her bound wrists, around her chest and in a "slingshot" around her breasts. Not tighly, of course, just enough to accentuate them and add to the helplessnes. A ball-gag completes her immobility, and she wears nothing but a thong. (I'm a guy...sue me.

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Now, knowing the way I am as a writer, I'm going to make this a 5,500 word short story if I let myself go here, so I'll give you the basics. I envision myself as a merciless tormentor given this girl as a "project" of sorts. In my fantasy, she was sent to me for punishment. There is no information to extract, no begging to be desired and no release planned until my work is done. I start out with a lot of verbal taunting...telling her why she is here, re-inforcing her helplessness and forcing her to think of every part of her body and exactly how it feels. I slowly let her realize that she is going to be tickled.
I spend the first of a very long time with unbearably light and annoying tickles that barely touch the flesh. I draw out the torture with finger-tip attachments that form long ponts. (Yes, I actually have a set of these). From her lashed elbows to the soft skin under her arms, I slowly trace a path of sensory destruction. Her entire body receives these effective but never-hard tickles from her nipples to her sides to her lower belly to her thighs. For her, time slows as these teasingly light yet effective touches drive her hysterical. I could spend hours describing how drawn out the foot tickling would be, but I'd never finish this...
At this point, I bring in another of my fetishes...forced orgasms. In her posistion, I use a ball-headed vibrator that fastens in a convenient notch in the platform. (It's a fantasy, remember? Convenient notches are all over the place! In real life, holding it will do...) After the first orgasm, I ask her if she's ready for it to be removed. Of course, she shakes her head yes. After the second brings desperate squeals from her, and the third sets her screaming into the gag...I turn off the vibrator and remove her gag. I tell her that there is only one way to make the vibrator go away. I turn it on again and listen to her beg me to tell her how. I get close to her ear and tell her to beg for more tickling. Hard tickling. I let another orgasm force its way out of her body and guide her along to say the things I want to hear...asking her why I should tickle her and what I'll get out of it. Mental-domination shit.
Once I'm happy that she's made the right decision, I give her a moment to breath and replace the gag, removing the vibrator. I start on her midriff, my favorite spot. I find the "sweet-spot" on her strethced bell just above the hipbones and place a single finger on each side, making small circles that press into the flesh. I tickle her faster and faster until she is moaning with laughter.
After that, it's pretty much the tickle-session from hell as I explore every part of her body and utilize every method at my disposal. Of course, the gag comes off after awhile for a few rounds of "It'll Stop tickling Here, If You Beg Me To Tickle You There".
Ok, now I need a cigarette.