Wow, I'm not sure... It's hard to choose. Perhaps it was walking into the control room of Middle Ear in 1985 and finding Michael Jackson, Diana Ross, Barry, Robin and Maurice Gibb and producer/engineers Karl Richardson and Ahlby Galuten there. Michael was the nicest person in the room second to Barry.
Another highlight was much later when I was working for AMS/Neve. We had just installed a baby DFC at Skywalker and George Lucas walked in and shook my hand.
Maybe the wildest was at Warner Hollywood when John Frankenheiner gave me a guided tour of his Merc 600SL that was totally maxed out. He showed me the engine and it was spotless. He said that he got all his cars detailed twice a week.