"I thought one less freerunner in the world would be a good thing"

For the second time in two days, I've had to walk past teenagers practicing what I think was parkour, though the walls in both cases were around waist height. It's good that they're getting exercise, I suppose, but they were going about it with such smug looks on their faces that I understand why traceurs always seem to find themselves being chased by people with guns.