How do you reverse engineer cool?

Like reverse engineering anything else, it boils down to observation.

    Find cool people.
    Observe cool people.
    Discover patterns.

Then, it's simply a matter of implementing those patterns.

You'll discover in the case of "cool" people, depending on the type of cool the patterns will be vastly different.

In one such instance, conformity is an underlying pattern. In others, its individuality. IE, school cool versus industry cool.

Only with the utmost studied concern for spontaneous authenticity.

You let cool reverse engineer you.