Cars where there's so many stickers on the rear window you know the driver can't see out of it. Rear cameras do not compensate because it requires more change of focus (and possibly button pushing) than using a rear-view mirror.
Not idiotic but just wrong: those "In Memorium to" messages. Nothing like depressing yourself every day while telling everyone else you can't get on with your life...while spreading a little depression to their day as well.