Exactly what it says on the tin.
My vote goes to the Toyota Prius. Yes, really. Not because its some horrible eco box, but because of the dramatic irony that surrounds it. Since the Prius uses nickel batteries, the nickel has to be mined, and that is ridiculously damaging to the environment, but more of that in a sec. Then its loaded on to a gigantic coal powered ship and sent to continental Europe where its refined in a large factory, then flown to China where its turned into the foam, and then flown again to Japan where is finally put into the cars. The amount of damage Toyota do to the environment mean they probably have to sell... I dunno, a rough guess... 4,000,000 cars to make up for all that damage? Even then, they don't produce that many, so they'd have to follow that entire process and ruin the earth even more. And the nickel mine...
Seriously, I don't care for the environment, but even I can tell thats not a small sacrifice for a car which was dubbed a "revolution" in motoring. Looks like a nuclear fallout to me. Plus, the car isn't even that economical. A petrol Fiat 500 will manage 70MPG, and thats about £5,000 less. The Prius, and all eco cars in general are useless gimmicks to make people think they're doing the world a favour, but they're not. They're gradually making it worse.
Seriously Toyota. Ditch all this eco bull and bring out the FT-86 or a new Supra. You might just spare your reputation then.