So, the recent holiday meant my wife and I were together with her family, which included her younger sister.
You can tell instantly that they're sisters -- they look alike in so many ways. Main difference is that where my wife has gentle curves, her sister is lean and athletic; she's kind of a little jock. They have very similar arms, for instance, pale with occasional freckles and a soft golden down all over, but where my wife's are kind of soft and rounded her sister's are more strong and angular.
And they're both well-acquainted with my ticklishness.
We were watching a movie on TV. It was a movie of my choosing and they were pretty vocal about thinking it was terrible. (It wasn't very good, actually, but I couldn't exactly admit that.) We were on the sofa -- I was lying with my head in my wife's lap; her sister was at the opposite end of the couch, near my feet.
I don't know how they orchestrated this; there was no evident planning involved. But the second the movie ended, the very second the closing credits started to roll, they both sprang to their feet and came together and loomed over me with shared mischievous smiles and started tickling me. It wasn't 100% clear whether this was explicit payback for making them watch the bad movie, or just an effort to salvage something entertaining out of the evening, or what, but whatever the reason, there they were, reaching toward me, the overhead light glinting on the golden hairs on their wrists and arms, and suddenly all twenty of their fingers were darting at my sides and stomach, scrabbling against my abdomen, and of course instantaneously I was hysterical with peals of wild laughter.
I couldn't defend myself -- I was outnumbered -- their fingers spidered along my sides, down by my waist, up across my ribs. I was writhing and thrashing on the sofa, unable to escape, my hands flying to each ticklish spot to try and defend myself but as soon as they got there the fingers that had been tormenting me there were gone, having flown to a different ticklish spot. My giggles were throaty and high-pitched, constant and helpless, thick with giddy desperation as they tickled and tickled.
A contented smile on her face, my wife serenely moved her hands from my stomach to my sides to my waist to my stomach again, effortlessly and expertly triggering each incapacitating tickle-spot with ruthless ease. Her sister took a more restless approach; she began by joining my wife in assaulting my twitching abdomen but eventually I suddenly felt her strong little hands gripping the tops of my knees, seizing and rhythmically squeezing them to send urgent depth charges of ticklishness shooting through me -- my laughter took on a new insistence, getting louder, getting more frantic.
"No, stop, no, stop," I tried to say to them, "No, stop," but the contours of the words were barely discernible, swallowed as they were in the billows of boisterous laughter.
The next thing I noticed through the haze of my forced delirium was a hand firmly gripping one of my ankles -- "No, no, no, no" -- and then my wife's sister's fingertips were scampering up and down the sole of my socked foot. My immobilized foot twitched wildly back and forth but to no avail, and my wife kept up her merry assault on my stomach and sides, and my back arched and I pressed my head into the softness of the cushions and I laughed and laughed and laughed and laughed.
Until finally they stopped.
"That was fun," my wife's sister said.
My wife gave me a kiss on the forehead.
And they left me to recover, red-faced and panting, alone on the sofa.
tickled my upper body without mercy. My armpits are still sore right now. In other words, it was wonderful! 
