By definition "Cool" is subjective, but for the most part it can be broken down to two things, the power of persuasion (verbal, artistic or musical), and leadership capability.
"Cool people lead" Musicians, orators and artists get pussy regardless of looks, the more innovative the artist, often the more pussy. They fill the need of spiritual guidance to the fan, according to degrees. Celebrities fall into this category regardless of talent or merit, but this is more a hollow modern phenomenon than anything that should fall under the heading of "cool".
Leaders get pussy and respect because they also provide guidance and direction.
The Fonz was a leader, he took no shit, he had a cool nickname that set him apart, he kicked asses, he fucked and fucked and fucked the beautiful young women up in his loft and Mr. C couldn't do anything about it because frankly, he was a pussy and was in awe as well. He kept him close so he could masturbate to the screams and the plaster dust that dropped on his face, while Marion was quietly fingering herself to the Fonz's image as she pretended she was asleep on the other side of the bed. And the Fonz played the bongos dammit, the coolest instrument of all times.
I stand fucking correctamundo goddamn it.