You must be kidding me. I had one person flash me an exacto knife in subway when asked to please move over so I could take an (available) seat.

Social norms are only effective in context of social consensus (or enforcement). Let's face it: we live in a rude and selfish society these days. A polite request only computes in a polite society. The person making the polite inquiry expects social support. So if that guy instead of shaking his head had politely asked the sociopath in question to "would you please lower your voice?", it would not be a surprise that he would then be subjected to a rude, loud, and personal attack by the said sociopath with little expectation of social support from other patrons. (Unless cgod is in the room, in which case ... ;P)

One ex: Just try walking in a straight line on sidewalks in NYC. Impossible. I used to be able to walk from WallStreet to MorningSide without bumping into a single person, and we were all zipping. These days can't traverse a lousy block without having to do slalom around sidewalk hogers. (And it is not merely the tourist or the "unwashed" -- in fact, this pattern now includes the "educated" class as well. I swear they are all still mentally and socially walking up and down the high school corridors.)