The classic case in point is the song "We Wish You A Merry Christmas", which starts jolly enough, but then begins to demand some Figgy Pudding and if they don't get any, then they're going to sing and sing until they get it. I've not even got a fig roll. This song is surely the "I know a song that'll get on your nerves" of the Christmas music canon.
And then from here there's the story of how I had an inner monologue that was singing mournful music while I was physically singing something more cheery.
With some more Googling, I found out that Microsoft have created Songsmith to automatically generate backing tracks to music for you.