I'm sure that everyone has his or her own story, but here's mine: I gave a talk at ASA (or maybe NoiseCon?) years ago. The subject eludes me, but I think it related to vibration rather than acoustics. Dr. Beranek was sitting in the very front row, in that green jacket that for some reason I always saw him wearing at conferences.
And after I'd finished my talk, he asked a Very Good Question.
I wish I could remember exactly what it was, but I recall it being deep: an inquiry into what something meant. I had purposefully avoided it in the talk itself because I wasn't yet sure that I had the right framework for interpreting it. And after a only high-level 15-minute presentation, Beranek had seen right through me.
Maybe somebody should put together a "Beranek Number" system, modeled loosely on mathematicians' "Erdos Number".