For me it has to be "MacArthur Park." According to Wikipedia: "In 1992, humorist Dave Barry conducted a poll among his readers (as recorded in Dave Barry's Book of Bad Songs) of the worst songs ever. Barry's readers selected Harris's version of 'MacArthur Park' as the worst song ever recorded, both in terms of Worst Lyrics and Worst Overall Song.
So, I'm not alone.
And with lyrics like those below, don't you think it's a perfect song to be stuck in my head on my birthday?
MacArthur's Park is melting in the dark
All the sweet, green icing flowing down...
Someone left the cake out in the rain
I don't think that I can take it
'cause it took so long to bake it
And I'll never have that recipe again