Getting changed out of my cycling kit, and back into my "normal" clothes, so I can get the tube and tram home. When I got on my bike, I found that the front brake block has just worn down enough that a hard application of the brake makes the cartridge holder hit the rim. Since that way leads towards (i) poor braking and (ii) a rapidly knackered rim, I've retraced my tracks.
So, changing into and back out of cycling clothes, plus walking to the bike sheds, unlocking and locking the bike, mounting and unmounting the lights etc all for nowt. Bah.