I have a few:
I happen to work in the marine lab where my neurobiology class is held. One day we got a big shipment of inverts from North Carolina Biological; during our break between the lecture and laboratory classes, my boss asked me to move the bags of anemones, polychaete worms, sea pansies, and various flatworms into holding tanks. Well, I wasn't really thinking and I put the Planaria into a 2 gallon with saltwater. I came back 2 minutes later to find their shriveled up bodies. I quickly told my boss and we ordered another shipment before even telling my professor they arrived!
Another time I was in the Everglades with my roommate, catching Mayan cichlids for his thesis. At one point on the 6-hour drive back, we decided to stop at a nearby ditch and do a water change for the 35 cichlids. By this time it was dark so we had to check for alligators with spotlights. After we determined it was safe we got a small section of garden hose and I was to start the siphon. I knelt down by the wheel on the pickup and pulled the water out. I guess it was a long day and I didn't know how fast it would go, because I got a lungfull of cichlid water from the bottom of the 100g container. My coughing was interrupted when my roommate manage to step on an old hoplo spine sticking out of the ground. Once he finally fished the 1" spine out, we couldn't find the first aid kit. It turned out to be a looooong night.