All-time ugliest car was the 50's model Volvo:
A few contenders for worst car of all time...
Vega and Pinto, obviously... Those two were deliberate. The bean-counters running Detroit in those days believed that they could not profit from selling small cars; the idea was to build two spectacularly bad small cars and convince Americans that they didn't want small cars.
AMC Gremlin, an aerodynamic disaster looking for a way to happen in any sort of a crosswind:
Triumph Stag, slow V8 sport car with cams which would warp out of a clear sky ("Swagger up to a Stag, and stagger away")...
Renault Dauphin: Public apology to the American people from French government:
Worst combination of ugly and dysfunctional, 80s V6 Volvo:
The V6 Volvos were ugly enough while not running. When running, they usually resembled a destroyer laying down a smoke screen in "Victory at Sea".
Humber Super Snipe:
Various SuperSnipe configurations featured clutches based on sand, magnetism, voodoo..
Early 60s Chrysler Imperial, power brakes and steering made car borderline uncontrollable:
Corvair Monza, Nader was 100% correct about this car, suspension was unsafe at any speed: