this sounds like it is about tickling someone dressed as the classical image of the female librarian - glasses, long sleeved starched white blouse buttoned all the way up, conservative skirt below the knees, nylons (nothing suggestive) and "practical" low heeled plain shoes, hair pulled back, maybe with a plain business-like jacket over her blouse. And she is prim and proper. And naturally, extremely ticklish and once the tickling starts she tries to maintain but quickly dissolves into uncontrollable laughter and squirming.
Put this in the list of tickle fantasies along with cheer leaders, Moms-I'd-Love-to-Tickle, haughty female bosses, sexy sorority coeds, women in uniform, and....well I am sure there are many more and I haven't even touched on the male entries into this tickle fantasy land.
If you look on Amazon, you can even find a Kindle ready tale about The Ticklish Librarian, part of an apparent series titled Tickling Tales of which this is #1, though I've never found other titles in the series. It is a graphic sort of story.