The LWS-6 Zubr
This plane looked as bad as it operated. This aircraft was only reserved for training drills (as it should have been) so they never saw the light of battle. Eventually, Russian soldiers stole a bunch of them after they invaded Poland. Luckily, they weren't really stealing much of anything...
The Saab 340
This passenger aircraft was an absolute nightmare for customer satisfaction. Any former passenger can probably still hear the horribly loud hum of the plane being pushed around by the air. Not only that, but the engine was so loud that people couldn't talk to each other onboard!