The coolest. Superior in coolness to all else. Used only when the coolness of something is definitive, classic, the model of coolness in its category or class. As in, Antarctica is the coldest place on earth, so anything which is cool is cool, anything way cool is way cool, but anything antarctic is the coolest.
Man, that's not cool, that's freakin' antarctic...
High tension between to people after an argument, falling out, break up etc.
After that break up things have been antarctic between you two.