One of my pet theories is that much time could be saved if on initial meeting you asked: which classic guitar group from the 60s/70s were you into as a teenager (and of course, this could be shifted to other genres depending on the context, say, which classic 90s hip-hop group did you like when you were 14-15 becoming human).
Again, the key notion behind this is which music did you like as a younger version of you. Obviously such childish things would be supplanted with time, made more various and subtle and possibly even mysterious, hard to gauge, but this initial passion - that moment when your self in development said yes, I choose this, this speaks to me - would continue to say something essential about the character of the person facing you today.
Now none of this is to say that those other musical choices were not respected, or liked by your younger self, but rather which one did you listen to under the blankets when your parents thought you were asleep; which one did you listen to when you walked to school to the point where you felt transfixed by it.
For me it was the raw intensity of the Stooges, with a major Bowie infatuation before this ... I even used to wear a silver bangle when I was about twelve-thirteen so I'd resemble him on the cover of Diamond Dogs. Strange girl-self.
But here would be another possibility, not for me, but others in the nascent musical-obsessive Melbourne milieu I grew up in: the Stones, though this group was never really of much interest to me (ditto, Jimi Hendrix, or the Beatles, or god forbid Led Zeppelin, or if you were a bit cooler, say MC5, though that'd be rare if that was someone's first love; the person is probably faking it).
If the guy, it was almost always a guy, said his first love was Black Sabbath, or Iron Maiden: this indicated something else entirely.
That part from just before 2'30" when it goes low to kick in with its full intensity is bliss, but the most amazing moment is from 3'10 when the bass-line/guitars gets funky with the drums, wow.
*There seems to be some debate about the location of the concert, some say London; some say Brussels.