Off the top of my head it's got to be the Pontiac Aztek.
It made me believe that Pontiac had to be full of "yes men" for a monstrosity like this to make production.


comments excerpted from the cartalk website:
The Plaztek has to be the ugliest hunk of polystyrene ever molded. Jeff
Let's face it, not every engineering student gets an "A". The "D" students need work also. Bob
One of our neighbors has a green one which we call the "toadmobile," which, come to think of it, is an insult to toads. Richard
The back end looks like it was stretched up too high, kind of like when an elderly person hikes their pants up to their chin. Eric
That didn't just get hit with an ugly stick; it came charging out of the ugly forest! Chris
It looks the way Montezuma's revenge feels. John
Looks like it was designed by two separate teams of engineers that started at opposite bumpers and worked their way towards the middle, each unable to talk to the other until they met at the center doorpost. Nate
Was Pontiac taken over by a high school shop class? Sam
It has all the style, grace, and sexiness of an orthopedic shoe. Byron
A horrid assembly of mismatched lines and angles, made even worse by the gray plastic body cladding of the "original edition." Richard
Just screams "committee." Thomas
Look like it has a wedgie. Lisa
Ever seen this car from behind? It's like getting behind a horse that's ready to drop a load. Susan
Looks like it went into the crusher before the showroom! The last step in the production process was being hit with an ugly stick. Nate
It is amazing Pontiac hasn't been sued for accidents caused by drivers spewing coffee over the inside of their windshields when Azteks drive by. Thomas