He grinned, and then chuckled when she remarked on it.
"Um, well... let's see... Cool is just a phrase that came in use. American English.... it's kind of like a lot of people watch the television and listen to the radio, and sometimes people on those use slang, just randomly. Well, if people like how it sounds they use it too and sooner or later everyone does. That is how cool started and how it came into use."