Just when I thought I had pretty much listed any and every possible inconsiderate passenger behavior on BART, a new observation took place to me that put me back to reality.
In the middle of a crowded morning train, a man seated near me took out a gold nail clipper and started clipping away his fingernails!!! Even worse, he didn't make ANY attempts to catch the sick clippings, or try to lower his nail cutting position to a more discrete angle. He was clipping away one by one at at chest-level while the rest of us watched his clippings fly away like ticks, one after another. It was sickening.
I would have said something but I was actually seated in back of him, so I wasn't directly affected by the clippings. I was also too tired to cause a scene, but even any of the nail clippings landed on my body, I would probably have yelled at him instantly.