Oh my God, I've only had that done to me about eleven gajillion times, and it always works. I can't not fall for it. It's pure wickedness.
One with a narrow range of applications but which completely destroyed me when it was deployed against me is this: the tickler's in a position to have to lean on you, her weight resting on her hand which is on your knee (as to lean over and talk to the person next to you) and then she begins squeezing. I made a ridiculous spectacle of myself.
I've been undone many times by The Cubicle: the tickler positions herself behind your office chair so you're wedged between the chair and your desk, and her fingers begin scampering down your sides, preferably while you're typing or using the mouse or (at its cruelest) on the phone. Abject begging ensues.
One of my former coworkers (who later, as it happens, became one of my ticklers, though not one of the more evil ones--she had too much empathy, probably) told of how her husband would come up behind her while she was carrying a huge basket of laundry, preferably up the stairs and start getting her sides; unwilling to drop the clean laundry, her only option was to shriek and laugh and try in vain to outrun him. Call it The Washerwoman.