I got given a t-shirt made for the Bicycle Transportation Alliance (based in Washington State, USA), which has a bicycle wheel on the front, and on the rear, in very large letters: "ONE LESS CAR". I make a point of wearing it as much as possible, although I never seem to get motorists hassling me about it. I guess all that horn tooting is just empty posturing, and they're afraid to confront people up close

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I have had one or two grammar purists pointing out that it should be "ONE CAR FEWER", but it just doesn't fit as well on a t-shirt.