[tux3]

Rationality isn't whatever people do. Biases are whatever people don't do optimally that they would, if they were perfectly rational.

Various subgroups can have different responses, but rationality is its own ideal, regardless of what people do.

[zwkrt]

In what sense!? From what god is Rationalty (TM) handed down? Which parts of society are Rational? Which of the sentences of mine is Rational?

Ostensibly Rational just means “with reasons” or “calculated” but there are many different calculuses under which one could operate.

I agree with GP. Economic rational agents are supposed to do things like maximize utility or minimize loss. I know that I for one do things like “anticipate others’ needs”, “feel ambivalent about eating the entire box of donuts”, and “take a day off work to practice origami”, and I’m not sure how those actions fit into the economic model.

[PeterisP]

It's not necessary to pull economics into the picture - the general definition is that a rational choice is making the choice that best furthers your goals. If you make suboptimal choices (with respect to your own goals - sacrificing "socially desirable" goals in order to achieve some desire of your own isn't irrational), that's an irrational choice, and people often do that for various reasons. We're not horribly bad at achieving our goals, but we're also nowhere near perfect. Some types of suboptimal choices are systematic, predictable deviations which we can study as biases.