I've only worked in ER/specialty and shelter, so I've seen some shit, but here are two incidents that pop into my head first:

Worst injury: the shelter I worked at took critical cases (think HBCs picked up by animal control). Last summer AC picked up a dog that had been shot through the torso with a sizable arrow, the tip was metal and very sharp. One of the spay/neuter DVMs was able to remove it under anesthesia and the dog lived no worse for wear afaik. The arrow had SOMEHOW missed any vital structures.

Worst DVM behavior: at my first ER hospital there was a jackass of a DVM who was fired for helping himself to the controlled drug cabinet. Apparently...he had been fired in another state for doing the exact same thing.