I had a neighbor with a SRT V10 Ram that I would pass on daily walks.

The rear spoiler was an upside down wing for down force. I think it actually increased total drag.

I as kinda shocked the first time I saw that a large number of the front radiator grille holes were blocked off from behind.

I now cannot walk past any car without aero thoughts involuntarily jumping up:
rear brake light shapes
spads covering half the rear tire
diffusers below the rear bumpers
placement of exhaust pipes on cars versus trucks that could pull a trailer

Like the joke:

Do Not think of a Pink Elephant !

In a similar way I now notice involuntarily
ear lobe creases in passing people as a sign of heart disease