The song, "Simply Having A Wonderful Christmas Time" by Paul McCartney actually makes me wretch. As to a few other of his pop nuggets such as "My Love (Does It Good)" have the same effect. It sure was a long drop from "Band On The Run" or "A Day In the Life".
Yoko was an art-house freak, and I have to lump most of Lennon's post-Beatle work in the pooper as well. If only Mark David had been born a few years earlier we would have been spared the Double Fantasy album.
Currently the worst thing that comes to mind is the incredibly lame, "1985" by Bowling For Soup.
Though some find him offensive, I really don't think Marilyn Manson deserves to be on a worst of list, particluarly if you take into account his Mechanical Animals album, which is probably the greatest Glam-Rock album since Marc Bolan died.