There are a few kits that regularly pop up on "Worst Model Ever" lists, due to age, poor design, or multiple remolds/modifications (and sometimes all three). I've had quite a few of these in my stash, and while some turned out better than others it's been fun to see how close I could get to a silk purse with these...
AMT '62 Corvette - nothing ahead of the front wheels looked right, from the tiny headlights to the too-tall front pan.
AMT '72 Nova SS - separate front fenders and badly bowed roof pillars meant that almost nothing looked straight out of the box.
MPC '69 Dodge Daytona - All the problems of their General Lee, plus an ill-fitting nose cone!
MPC '67 GTO - just, ugh.