If memory serves me correct, the first time I recall it was in a Pink Panther cartoon @1970. The Pink Panther is conducting an orchestra, possibly at the Hollywood Bowl, and after he finishes the concert, he sees that there’s only one (enthusiastically applauding!) person left in the audience. Before we see the sole attendee, I think there’s the sound of crickets chirping.
Anyone with any earlier cite?
(This is actually a GQ, but I suspect it would end up over here, anyway.)
Oh, and the one person left watching the concert: Henry Mancini!