This is a column about waving. Specifically: waving hello while riding a bicycle, or going for a run. We are approaching peak season for recreational cycling and running—if you do these things all year, you may be astonished by all the newcomers out there, filling the roadways, adopting the habit, desperate to burn off the lobster rolls and margaritas—and no matter where you live, you are going to encounter someone cycling or running toward you in the opposite direction. It doesn't matter if you live in the city or the most desolate place on earth (a Miami Marlins home game). Eventually you are going to be faced with...