The game does not have a single button labeled "Randomize Everything." You have to engineer the chaos using the settings below.
With the Randomizer, every video is a "First Look."
If you are looking for specific "randomized" themes, try these popular community setups: The "Worst Case Scenario"
The biggest killer of racing game longevity is "decision paralysis." You sit down to play, spend 15 minutes scrolling through 180+ cars trying to find the "perfect" combo, get bored, and quit.
After running thousands of random races, here are the five worst (and best) combos I have generated. Try them if you dare.