Nail clipping on public transit--why???

I was sitting on a Caltrain on my way home from work yesterday, reading a book and minding my own business, when I heard a sound behind me that shattered my peace--the sound of fingernails being clipped in public.

People clipping their fingernails on public transit is my number one pet peeve. Why?

1. The incessant "clip-clip" is so annoying.
2. Fingernail clippings go flying everywhere, no matter how careful you are.
3. Lots of germs and dirt reside under fingernails--I do not want to be sitting in your germs and dirt.

In short, it is disgusting and downright inconsiderate. Apparently, some people don't seem to realize this. What is it about a train or bus ride that compels them to pull out their clippers and start giving themselves a public transit manicure?

It took all of my will power yesterday to not whirl around in my seat and tell the woman behind me to STOP. But perhaps I should have, I would have been doing the public a favor.