DeLorean Time Machine
The DeLorean model was once a futuristic sports car made by the company of the same name. Now, it looks like an old car that's lost its glimmer with cool doors. It doesn't look very pretty anymore. Furthermore, it breaks easily (after all, Back to the Future wouldn't have problems going back to the future if the time machine hadn't stranded them in 1955). The anti-theft protection is also low and it's fairly easy to steal. The DeLorean is dangerous as well; it has a small nuclear reactor in the back, which is deadly in the event of a crash. This invention needs some work. However, it does eventually return everyone to their proper time. Nevertheless, its appearance and other serious flaws make it the worst example of time travel design.