Auto fads that can just stay away - they were bad then and they'd be bad again.
One of the worst I can remember were the colored bent plexiglass bug deflectors that people would mount on the hood of their half tons to look like a big truck - I remember people making them in high school shop class and then drilling two holes in their truck's hood and mounting them with a couple of bolts - dumbest thing ever but at the same time, it would be kind of cool to see a 70's era half ton with one mounted on it at a meet.
What auto fad would you like to see stay away/not have a retro resurgence?