I try not to ride on sidewalks, but at one point on my commute there's a confluence of one-way streets right where I stop for food. I can either ride three extra blocks in a big circle, or I can hop on the sidewalk for half a block and lock up in front of the store. I have always chosen the latter. To make it seem slightly less wrong, I'll coast at about the speed of a fast walk and then swing one leg off towards the end and glide in. Yesterday I was pulling right up to the rack and there must have been a small rock on the sidewalk. I'd just pumped up my tires, and my bike was at the perfect angle. When I ran over it, the rock shot out from under my tire like it was blasted out of a slingshot. It went right past a police officer checking parking meters and blasted a Toyota Prius with a loud "TWANG." I looked at it. The officer looked at it. And the car's owner, standing inches from where the rock hit the car looked at it. We all sort of hesitated for a half-step, then I bent to lock my bike, the officer kept looking ahead, and the car owner just stood there. When I came out of the store two minutes later, him and the car were gone. I half expected my bike to be backed over with Prius tire marks on the frame, but he must have decided to cut me some slack. Or maybe he just threw a rock at it and called it even. Either would have been fine with me.