I love the idea of a girl that knows you have a tickle fetish provoking you and teasing you in a public setting, like a beach date. Maybe she has tickle fetish of her own, or maybe she doesn't, and as a bit of revenge for all those times she's let you indulge on forcing her to laugh until she's crying, she has decided to enjoy making you squirm for a change. Simple stuff like dangling her sandals leisurely, letting you catch glimpses of her soles, or yawning exaggeratedly and displaying her perfect armpits for you is already enough to get you hot under the collar, and she knows it. She knows you can't stop glancing and her sly smile all but confirms it. But the big guns come out when she asks you to help her with the tanning oil. She asks that you don't miss a single spot, and spend as much time as you want anywhere making sure you get it right- but be careful, she's really ticklish, she reminds you. And true to her word, anywhere you touch, she jolts and giggles cutely, a sound she knows you can't resist. The urge to dig into her sides, or squeeze her hips, or wiggle your fingers under her arms and in between her thighs until she's screaming your name with laughter is unbearable, and nothing is stopping you really, she's not resisting, she's all yours, down to her wiggling toes... But be careful anon, people are watching. Families with children, enjoying a peaceful time right there, on the next spot over. You wouldn't wanna make a scene, right? A woman screaming with laughter is bound to turn a few heads, and more than a couple might notice her boyfriend is getting rock solid just from giving her a few tickles.
She asks that you give her a second coating right under her arms, but that you try not to use your nails this time so you don't make her squeal so loudly again. Oh, and maybe later you could try to bury her in the sand, maybe leave her feet out, just for fun. She thinks it could make for a couple of cute pics, but you're going to have to take them since she's going to be all but completely helpless, able only to wiggle her toes...
And all the while her seductive eyes confirm that she knows it as well as you do: that when you go home and you finally have her all to yourself, there'll be hours and hours of laughter to pay.