For a couple decades I lived in a city that had walnut trees lining many of the old county roads (legend has it they were planted by/for the women's auxiliary so that their grand-daughters would have shade on their Sunday carriage rides). Many cyclists, myself included, made a habit of purposely launching the walnuts at our fellow riders. We actually got pretty skilled at bouncing them back and forth off the front spokes. Of course that would be a lot harder to do in these days of minimally-spoked wheels.