Out of nowhere, a co-worker at a previous job suddenly broke into the chorus of "Alexander's Ragtime Band." There was no ragtime music playing at the time, no one in the office named Alexander, or any activity at work that matched the tune's rhythm. It wasn't a bad rendition; it was on-key and very spirited. I still have no idea what prompted it.
That incident, however, made me less fazed when she broke into "Look At Me, I'm Sandra Dee" abruptly about two years later.