I Know What It Takes To Be Cool
Prison inmates aren't allowed belts because they can be used as weapons, and so we have low-riding as a statement of belonging to a certain group.
Shirts untucked, or worn open over t-shirts, imply concealed weapons.
Soldiers have, by regulation, short hair. So, long hair is a signal to distance oneself from the armed forces, a socially polarising move when war is a current or recent concern.
Fashion is irretrievably tied to notions of class identity. The poor try to look rich, the rich try to look super-rich, and the super-rich try to look poor because it amuses them.
‘Coolness,’ in the original and more literal sense – an affected apathy – comes from the Jazz age, as black performers chose to keep the often horrible circumstances of their lives concealed behind a mask of uncaring.
Form your own conclusions.
(The title refers, of course, to Stewie Griffin's perfect re-enactment of William Shatner's sublime performance of ‘Rocketman’)