Walking on Air by SG (Archive Link)
This story is one of my favourite Hidden-in-plain-sight stories ever. I found it pretty early on, and it has stuck with me ever since. The story follows the female narrator on her flight to spend her New Year’s holidays with her collage friends. For her flight, she just has some fun additions prepared, which she needs to set up in the airport toilet. A combination of inflatable dildos, long tubes and some pumps allow her to constantly change the size of her inserts by standing on the pumps she has placed under her feet inside her shoes. One can imagine how alone the walk to the air-plane goes for her, constantly getting fucked by her inserts, with no one around her knowing what is going on.