After posing the question back in 2003, noted social theologian André 3000 answered with the immortal, but somewhat perplexing, "Ice Cold!"
While I'm not going to argue with dre, I'd like to present another possible solution.
If this ain't cooler than being cool, then, well, nothing is.
The fact Frank Sinatra was The Man is not up for debate.
Watch the clip. It's pretty much the blueprint for being a smooth smoothie. You don't sit there with your cigarette like he does if you are not at the top of your game. And at this point, Sinatra most definitely was. This was still early days for television, and folks were still working out how to carry themselves on screen. Ice cold? Indeed. That he introduced the average American to another one of the coolest men ever with so much class speaks volumes.
Tom Jobim invented bossa nova, and is one of the most influential composers ever. The city of Rio de Janeiro re-named their airport after him: he was just that sort of cat. But he would have been virtually unknown in America at this point, so Frank getting him on national TV to do their thing together was a gracious act.
What makes all this even cooler is the mystery surrounding the album they recorded together. For reasons unknown it was cancelled, and Warner Brothers ordered the destruction of all the tapes. Apparently there are fewer than five original copies still in existence, but if you're into this sort of gear, you can dig for it online. It's worth doing.