The worst car I have driven is my mom's old Hyndai Pony.. circa 1986 or so. It had trouble getting up the Alex Fraser Bridge, and it quickly lost third gear entirely. The warranty was pretty damn useless, as it turns out. I felt really bad for her because that was the first car she had ever bought for herself.
My own personal worst car was the 1978 Acadian (Chevette). Bright lemon yellow (because it cost more to change the colour). That thing went through about 3 starters and ignitions, and SQUEAKED TO DRIVE YOU MAD!! Batty, I tell you! the hatchback floor was metal, uncarpeted, and every single bump in the road caused the hinges and screws to set up a racket.
At least it was easy to break into and easy to find in the parking lot. Bought it for 800$, sold it for junk about 3 years later.