While not nearly as rude as an uncovered sneeze, a loud phone conversation (unless it involves a girl crying over matters of the heart, which is a richly satisfying eavesdrop), a protruding backpack, or this, we ask Muni and Bart patrons to refrain from using public transit as their personal nail salons. Clipping your fingernails (or, God forbid, toenails) is gross to watch/hear while riding home. So: don't.