As Brad rode along on his single-speed, he picked up a Remora. Like the parasite fish who attaches himself to a shark, riders on racing bicycles who suck your wheel on the bike path take advantage of your strength in order to make their lives easier. It is bad manners to draft without an invitation.
Eventually, Brad dropped his pace a bit, forcing the other rider to either slow down, or pass. The Remora blew by, without so much as "Howdy", and forged ahead. At this, Brad stepped on the gas, planning on returning the favor and drafting off of the inconsiderate rider.
Just then, an errant shoestring wrapped itself around the axle of one of his flat pedals, and forced Brad to coast to a halt so that he could disentangle himself. The Remora faded into the distance, and Brad continued on his way.