Righteous:  upright, moral, justified.
Self-righteous:  confident of being righteous.

Righteous is positive, while self-righteous is negative.  Yet shouldn’t we expect a correlation on average between how righteous someone is and how righteous they think they are?  Sure it is bad to be over-confident in one’s righteousness, but could we be so bad at estimating our righteousness that people who think they are more righteous than average are in fact less righteous than average?  How could this be unless we had almost no ability to evaluate the morality of our actions?  And if we were this morally blind, why bother to consider morality, as our acts would on average be just as moral if we ignored it?

Yesterday’s Washington Post suggests there is in fact no correlation, because of some very arrogant very immoral people:

When two researchers recently asked people whether they felt they were moral, and then asked whether they would ever cheat on a test, those who said they were the least likely to cheat turned out to be the same ones who had the strongest conviction that they were moral. No surprise there.  But when the researchers looked at the group who said they were the most likely to cheat, they found to their surprised that this group, too, had strong convictions that they were moral. Those who lacked a strong sense that they were moral tended to be iffy about whether they would cheat. …

People with exceptionally strong convictions about their moral goodness are likely to follow extreme courses of action because they can convince themselves that whatever they do is good. When the right course of action is ambiguous … such people are likely to gravitate to opposite ends of a range of behaviors. When there is wide social consensus that something is wrong, they tend to conform to social norms.

When the researchers tested their hypothesis on managers who were asked to make a judgment call involving a conscientious employee who needed to go home early one day, they found that the managers who believed most strongly that they were good people came to extreme conclusions: They either let the employee off for the rest of the day with full pay, or insisted the employee stay and work full hours. The managers who did not think they were particularly good people tended to reach moderate conclusions: They had the employee finish some work and then leave early.

More here.

Added 8Nov: On reflection, the simplest explanation here is just that bragging is a bad sign.