In my opinion, it got to be this one, the W87H. It reminds me of a G-shock without its resin skin, looks unfinished and fake in some extend. It's actually a genuine Casio product, that's still available for $15-20 new today. But once you look at its specs (W87H-1V - Sports, Mens, Womens, Ladies, Digital, Analog Wrist, Watches | CASIO America, Inc.), you will realize even at that price range, it's over priced! 60 min stopwatch only, com'on, in this day and age? Even for $15, you can find Casio's with better stopwatch and timer.
So what's your opinion for the worst Casio watch ever made? We can find all the praises in this forum for their watch products, but there got to be one that doesn't meet the eyes or expectation.