The rise of the smartphone has led to, in NYC at least, large numbers of people stopping short on the sidewalk to send texts/emails. That's usually unfortunate for them if I'm walking behind them. It turns into Godzilla rampaging over Tokyo 'cause I'm sure as hell not stopping on a dime to avoid contact.

I also love the ones who stop in the middle of the steps to the train station, effectively blocking people from going into/out of the station. Those people make for more interesting road kill.