I think it's EXTREMELY SEXY watching my fiancee trying to resist as I slowly tickle her most ticklish spots - feet and underarms, and both hold still and not laugh. I absolutely love resistance games. Her face starts to scrunch up, she squeezes her eyes shut, her lips quiver, toes begin to curl, then I go in for the kill and she explodes with giggles. But usually before that she starts to hum or make noise to distract herself or something. That's how I know I am getting through her defenses.
Man, I would kill to have her tickled by a professional tickle Dom. She's agreed to it too. We just can't find anyone. I bet a professional would be able to drive her up a wall. I'd kill to watch that.
I have tickled others in the past as well and I find the facial expressions right before they crack to be most pleasing. Similar to what I described with my fiancee it's typically eyes squeezing shut, mouth tight lipped until a smile begins to form and suddenly the floodgates open. Haven't had too many lees like that though. It's either straight to giggling or silence and wiggling. Hey, that rhymes.