I've had "March on Cambreth" (by Heather Alexander) running through my head steadily for six hours now. Trying to hum something else doesn't help in the slightest -- Cambreth simply swings a metaphorical axe at the other song and knocks it dead. Evil, evil song.
(Okay, so it's partly my fault for listening to it four times in a row in the car. But it's so much fun! If they ever make a movie about the comic book Slaine, this absolutely has to be the main theme...)