When I tickle vanilla women, say on their feet for example, I have learned to start by deliberately tickling them in the most ineffective way possible. Maybe I’ll slowly but with some pressure drag the pad of my index finger (not my fingernail) down her sole or some other ludicrous non-ticklish technique.
“You’re not ticklish?”, I’ll say, and then I’ll get some answer like “nope” or “not right now, I guess”. I keep it up for a few and then seem to get frustrated and challenged. “Dammit, I Know you HAVE to be ticklish!” And then I’ll keep at it but slowly ramp up the intensity.
This makes for a nice long tickle which I love, instead of a quick swipe, a squeal, and it’s over. Also, she’s trying to fight me and the tickling, which I love. I usually get what I’m after - laughter - eventually, but it’s nice and drawn out and there are some sweet facial expressions and even sometimes tickle talk along the way!