The way I remember it, a comedian was talking about '70s porn and mentioned that “You always knew when the sex was about to begin because the gardener would come in from outside and ask for a drink of water. And then the music would begin…”
Since Lynx (UK) and Axe (US) have started using it as the basis for their ad campaigns, it’s going to be hard to research this. But I know that I was hearing stand-ups use it in their routines in the very early 80s, when I aspired to be a stand-up myself.