Well, apparently this doujin fell off the end of the earth into a black hole because it shouldn't be hard to find but it's nowhere. It was a chikan + scat "parody" of some pop manga don't remember if K-On or something similar, there was a cannon chubby (Japan chubby, not bbw) Hschooler with her friend on the train, they get there barely in time and while chubby's half asleep resting on her friend (who is kneading her) the friend starts getting molested, then when things heat up and chubby notices she says it's the best part of the train ride and common doujin plot unfolds. Given the tags it should be easy to find but nope, disappeared everywhere...