The vertical doors on Tesla SUVs. Doors are actually one of the most complicated parts of a car to manufacture and make reliable, and those doors are widely credited with why the shipments were late. In addition to people complaining about their reliability and their absurdly high cost, they provide no real benefit. Supposedly you can park in tighter spaces and get out, however the front doors still open like regular car doors. So assuming the driver also wants to get out, it's pretty fucking useless.