No surprises there, really, other than the Mustang II, which I'll get to later. Warning: I'm about to write a book post...
Fact: this is the car that made me hate Pontiac until I got back into cars three or four years ago. Oh the irony in that. Had it been decently styled (I've come up with a decent fix now to just get it on paper), the Aztek would have been a decent car. But this and stupid GM policies are the reason my beloved Pontiac is now dead.
The Yugo and Pinto are obvious choices. Their failures are known well enough that those two spaces could have been used to list different cars.
I didn't know about the Vega's issues. The Vega has good looks though and I'm sure if you dropped a 305 under the hood it'd make a decent fair weather car.
The Ion? Well that's obvious enough it is a Saturn after all. All the money GM put into Saturn could have been used to keep Pontiac alive.
The Edsel. Where to start on that? Oh Robert MacNamera. Pro tip for JFK: Just because he could kill off Edsel and save Ford money doesn't mean he's gonna be a good Secretary of Defense.
Cimarron: I can't believe there are people out there who actually like this leather clad Cavalier. (Chevy and Vauxhall Cavaliers share nothing except for name)
Making a diesel Cutlass was probably the second or third nail in the coffin for the Cutlass and for sure was the first nail for the Oldsmobile brand. Oldsmobile should still be here today. Buick should have died instead.
Ok now for my Mustang II rant. Look we as car lovers all know this is a horrible car and the worst Mustang out there. (SN-95 haters can go disembowel themselves) But if you had a Mustang II you could make it sporty like it should have been. And you still get to tell all your idiot non car loving friends that you own a Mustang. Maybe I just feel bad for the Mustang II, I don't know, but look at the sales figures for it. Clearly it had some sort of appeal.