In various discussion forums, on various communicator platforms and in cartoon pictures the 'cool' smiley is the one with 'dark glasses'. Is being 'cool' associated with dark goggles? I would say yes. What other associations support this idea?
Secret services agents on small and big screens, mafia dons, martial arts fighters and other heroes are seen with dark goggles. I asked some of my friends about the relation between goggles and looking 'cool'. I received many responses. But before having asked this question, I asked them:"Do you think that there is a relation between looking cool and wearing dark glasses?" It seemed that all of them were affirmative on this. Then as I asked them about the reasons-one of them said that "It makes people appear better and hence cool." Another said that it saves eyes from sunshine and makes them cool.
I have observed it in movies and TV serials that in the grim settings, the character with most cold heart would wear dark glasses all of the time. I hypothesize that except for blind people, movement of eyes is very highly associated with the change in emotions. If you're not given access to changes in eyes of the person, during a real-time interaction, it becomes exceedingly difficult to sense his emotional state, even if you are able to discern his facial expressions. Charisma, which is a more specific term for more popular urban term 'cool'(you might not agree, then, you might answer the question if charisma is associated with dark glasses) is all about being calm and composed in almost all situations. The dark glasses, in my humble opinion, don't let others gauge change in your eye movement, projecting an image of charismatic individual.
This is just a hypothesis. I would like to hear your opinion on this.
A similar proposition is: Contribution of black cloaks in making people look mysterious.
Image Source: Here