Tonight the players determined that it was one PC's birthday (because it was the player's birthday). So as a present, the PCs cast a spell so that their lives were a musical for the day.
And so our role-playing session became an improvisational musical. Everyone burst into song and choreographed dance numbers.
Everyone except the jerkass NPC Trent, who had a spell to protect from mind control. He assumed he was having a stroke or had been drugged or something when everyone started singing.