If it weren’t for his furtive, occasionally darting eyes, Mile’s Davis’s 1959 performance of “So What?” (see below) might serve as an ideal video embodiment of the word nonchalance.
I.e., the projecting an aura of a relaxed, confident detachment.
It seems as if no one’s all that into it, maybe not all that interested.
For example, at 2:41, notice Coltrane looking impassive in the background during Miles’s solo, eventually, however, nodding his head in half-assed admiration.
When Coltrane begins his solo, Miles splits for backstage. At 4:28, check out the two white fellows behind Coltrane actually conversing, seemingly deaf to gorgeous notes streaming from the tenor saxophone five feet in front of them.
At 4:40-ish there’s Miles himself in the background smoking a cigarette, detached.
At 5:03, though still offstage, he’s back into the flow of the music, swaying.
Throughout the entire performance, you see people who should be behind the scenes casually milling around, talking.
The obliviousness to momentousness of the music reminds me of that Auden poem describing an “untidy spot” on the canvas of an Old Master’s painting depicting an unnamed martyrdom where “dogs go on with their doggy life and the torturer’s horse scratches its innocent behind on a tree.”
Anyway, when the camera’s on Miles in profile, his body appropriately takes the shape of a question mark.
It’s like Miles is cool cubed, which being too too too cool, threatens to heat up into violence.
There’s tension, calculation in those eyes looking backwards into their skull. They’re not looking at what’s ever opposite of them in that studio.
But it’s the music that really matters. Check it out for yourself. The trumpet saying so what, so what, so what.
Do it, Miles.
 I’m imagining an on-line dictionary that provides multiple multimedia examples so that you really get a feel for the word
 My definition.