Longshot, /r/:

I remember finding a doujin wherein a chubby, undersexed school nurse ends up in an undersized school swimsuit and pigtails, and nails a few of the students. It starts with her smoking outside, listening to the younger teachers talk about hitting their students.

If anyone could point me to the artist or to a doujin, they'd be a miracle worker. I think e-hentai had it, but I can't find it now.