I once dropped a 35–200mm telephoto zoom in a canal in Venice whilst fumbling to change lenses. I tried snatching it when it slipped off my hand, but hit it instead, causing the lens to bounce off the balustrade and disappear into the depths. KABLUSCH!()
It was a relatively inexpensive lens, which came with the Canon kit my mum gave me for my birthday, but I did feel quite angry and stupid!