To me, it's pretty obvious "cool" can only be defined descriptively, not prescriptively — i.e. "cool" is whatever makes idiot teenagers intuitively, instinctually impressed with you. By definition, you can't tell idiot teenagers what to think — in that, once you successfully do that, they're not idiot teenagers any more, and so are no longer the arbiters of "what's cool."
To me, it's pretty obvious "cool" can only be defined descriptively, not prescriptively — i.e. "cool" is whatever makes idiot teenagers intuitively, instinctually impressed with you. By definition, you can't tell idiot teenagers what to think — in that, once you successfully do that, they're not idiot teenagers any more, and so are no longer the arbiters of "what's cool."