"Worst pin" lists are a lot like "worst music" or "worst book" lists -- the worst pin I've played is probably so forgettable that I've, well, forgotten it. Something has to have a certain level of quality to even register in long-term memory as "oh, geez, that was bad."

That said, there are four games that would tie on my list of "worst pins I remember playing", for different reasons:
* BBBB, because I couldn't understand what I was supposed to do.
* SF2, because I understood what I was supposed to do and I didn't like it.
* Police Force, for its "take high score" feature that utterly destroys the rest of the game. (Bride of Pinbot gets a solid honorable mention -- not for the billion shot, which bumps you to a different high score board, but for the 50M Big Wheel award.)
* Super Mario Bros, for the combination of "not at all fun to play" and "not at all fun to stand within earshot of someone else playing".