Hey - this is supposed to be a collection of worst songs :)
Fairytale is definitely my all-time secular favorite - I just wish the language was less vulgar (could have still gotten the point across).
Now, as for worst, I am surprised no one has mentioned Silent Night/7:00 news.
I have found that song--in which Simon and Garfunkel sing "Silent Night" while a reporter broadcasts the news in the background--to be not so much bad, but weird. The news broadcast is from around August 3, 1966, but I don't believe that all of the events mentioned occurred on the same day--and I'm pretty sure the broadcast wasn't delivered by a real newscaster.