What does it mean to be cool? There are various aesthetic definitions you can use, and none of them are wrong, but is there an essential, moral element of coolness that we're overlooking? Can coolness actually be a virtue?
Etymologically speaking, Old English speakers used the root word col to refer to "unperturbed, undemonstrative" people a thousand years ago, so it's not as if the association between moderate temperature and temperament is a new one. And the fact that it didn't originate in religion or moral philosophy, and has never been explicitly defined as a virtue in denotative terms, isn't really relevant; most valuational terms don't and aren't.
U.S. marketing scholars Caleb Warren and Margaret C. Campbell recently took a critical look at six studies on coolness, and specifically the relationship between coolness and autonomy. What they found was that a brand or individual's coolness factor was based on their ability to disobey unnecessary rules while still conforming to necessary ones. Based on this finding, they defined coolness as the ability to be "autonomous in an appropriate way." I see two two problems with that definition: one is that it's a little bit circular (if you're autonomous in an inappropriate way, nobody calls it autonomy), and the other is that there is really no such thing as general autonomy. One is always autonomous (or not) in relation to something, or somebody, else.
Using the Warren-Campbell findings, I would define coolness a little more casually: coolness is the art of being pleasant or commendable without making any discernible effort to do so, revealing in the process that your values are not contingent on the approval of others. It is a subtle display of power, courage, and maturity, comparable in some respects to the Taoist concepts of wu-wei and "diminishing will." A cool person pleases people without being a people-pleaser, impresses people without trying to be impressive, and so on. The etymological connection to moderate temperature is quite clear: something is cool if it's neither cold nor warm, indicating that it's not affected by outside elements.
Violating unnecessary rules, while obeying necessary ones, has nothing to do with appropriateness and everything to do with having an internal locus of control that still satisfies the moral requirements of the community—it shows that while your values are in alignment with the important rules, you don't depend on the rules to determine your values. Coolness doesn't create power; it displays it. A brand is cool where it can actually afford to dismiss unnecessary rules; Apple CEO Tim Cook's recent remark to the effect that they don't want investors who don't acknowledge global warming was cool because most companies aren't willing to risk alienating investors. Apple is big enough (or, to whatever extent a corporation can be, courageous enough) that it can. That's a casual display of existing power in violation of an unnecessary rule in a way that doesn't offend the values of the target audience. That's cool.
But if you focus too much on coming across as cool, you run the risk of jumping the shark. The Happy Days producers found that the Fonz, a supporting character, was so cool that he became the fan favorite on the show—so they exploited this by trying to make him cool enough to justify all the popularity, ruining the character (and the show) in the process. Their characterization of him removed the appearance of an internal locus of control.
And if the Warren-Campbell theory is accurate, it's probably no coincidence that sunglasses have become a casual symbol of coolness. The message they send is that you literally don't care whether people can look you in the eye—that you have the power and/or the chutzpah to completely disregard that element of social interaction in favor of your own comfort and fashion choices. Of course, if you wear sunglasses in an effort to try to look cool, all bets are off.