one of my favorite tickle tropes is tracing/connecting the dots with freckles/moles
like person a has a ton of freckles or moles on their neck/back/chest/belly and person b is obsessed with them
and loves to trace their fingers between them, making person a squirm and giggle and go to push them away
and b is like, “let me connect the dots!”
and with their finger or maybe even a marker they connect the spots in no particular shape, loving the light laughter and attempts to wiggle around from person a