With all the desired/best theme posts, i started thinking about what some of the worst themes that could be made into a pinball. Below are a few I came up with.
Sports – curling, cricket
Vehicles – Geo Metro or Yugo, Unicycle racing/rally
TV/Movies – The Bodyguard, Glen or Glenda (was thinking Plan Nine originally, but that could actually work), Infomercial Classics
Music – Baroque or New Age Classics, Zamfir, anything with bagpipes (and I actually like bagpipes)
Culture/Society – Serial killers, Hello Kitty (please don't tell me there is one), Hanging Chads
Science/Nature – Fungi, Physics