Public transportation is not for the faint of heart. People are gross and just when you think you've seen it all, you will see something even worse. Subway riding in NYC included seeing homeless human beings taking a shit. Here in Portland, people get murdered on the MAX by a deranged, knife wielding white supremacist. See, now a nail clipper doesn't seem so bad.

4 - Also, don't clean the lint from your belly button in public.