What is coolness, why does it exist?

I wouldn't say coolness is just for people. Animals can also try to be cool. I had a cat that wouldn't come in from the back yard so sometimes we had to grab him. When we got to the door of the house, he refused to be carried through the door in front of the other cat standing around. If the other cat wasn't present, the first cat had no problem being carried in. He was being cool!