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You know that $88,000 BMW 8 Series coupe that cut you off in traffic the other day? If you regarded that vehicle as a public menace, you might have been right — economically speaking. Economists regard show-offy luxury items like a high-end Bimmer (or a Maserati, Mercedes or Jag) as a “public bad.” These are items that might produce positive effects for the delighted owner but have negative external effects on the wider world: A fancy car inducing envy in others is an example of a public bad. Compare that to a public good, such as when you shovel the entire sidewalk so that everybody gets to use the path, not just you.