Female exhibitionist teacher on a bus, 1st person (I think.)

[GenAlexander]

I probably read it at least a decade ago.
I remember reading a story where a female teacher masturbates and then gets on a bus or some other public transportation vehicle with her students for some sort of a trip. There was no actual sex, I think, just her being horny and maybe flashing a bit. I feel like it was in first person.
It was only one chapter and it had some sort of a disclaimer inviting readers to continue the story as the writer lost interest.