Today's pet peeve comes in reporting of public acts of violence, and bystanders not intervening. Generally, some horrible act occurs in the public square, and the news accounts inform us that "one hundred people looked on but did not intervene" or something like that. The Kitty Genovese murder is the archetypical case, but you hear it pretty frequently. The implication is amazement at how many people could be so callous and uncaring -- could not one of them have the decency to stop the atrocity?
Ladies and gentlemen, allow me to introduce you to a social psychology phenomenon known, conveniently enough, as the Bystander Effect. The Bystander Effect tells us that people are less likely to render aid to those in need when there are many other people around than when they are alone, and the effect is compounded based on how many bystanders are present. So, if C observes A beating up B and C is the only other person present, C is far more likely to intercede than if C is there with a dozen other people present (and even more likely than that if there are a hundred witnesses). There are several reasons for the effect, mostly having to do with issues of conformity, but it is a pretty robust finding.
So the next time you see a story like this and conclude that "wow, one hundred people and not a halfway decent human among them", remember your psychology and think for a moment. Now you're more educated.