I have to admit, the Pacer is hard to top... I mean, bottom?
Worst ever? My girlfriend in high school owned a yellow Gremlin. Making out in the trunk space of a Gremlin? Bad idea.
Personally owned? A 1976 yellow Ford Pinto. I remember as a kid: road trip through South Dakota in the height of summer with no A/C. Yikes.
Worst line of automobiles overall? AMC. Pacer, Gremlin, Javelin. Say no more.