Where I work, every year we have free pizza for lunch and this year one of the employees will be reciting the first 3,141 digits of Pi. (I think he knows more, actually.)
Something like this happened to me once. I was playing trumpet in a small Rhode Island community orchestra, and we were rehearsing at the RI Community College campus. While we were rehearsing the Star Wars theme, in walked Darth Vader. We all nearly had heart attacks. This was not planned --- rehearsals for some minor modern play, in which Darth Vader was a character, were taking place down the hall and the actor decided to wander in when he heard the music.