cool means you appear confident, attractive, and socially effortless even if there is effort behind the scenes. the meaning has been stretched to mean "socially desirable" which is a slightly broader category
Confident, attractive and socially effortless are all highly socially desirable traits in a friend or mate. This is obvious to anyone who isn't socially problematic. I can tell you've never been cool!
Who's stretching the definition of "cool?" Cool is a social convention, not a scientific term.
The bottom line is, "people" don't like being around anxiety-riddled individuals with social hangups. They like people who are "cool."
The worst thing you can do if you want to be cool, is get upset about how other people are telling you you aren't.