I can't say I've had any real tragedies but once, when I had a 'three tier' setup, actually a deck, some chairs, and the ground, I totally goofed. I only had one pot, a cooler mash tun, and collected wort into buckets to transfer back to the pot. I had just doughed in, letting the strike water flow from the pot on the deck to the mash tun, stirred really well, and immediately began to fill the pot back up with sparge water. I was cutting my tap with bottles of distilled water, so it took awhile. Once I put in what I thought was about 7 gallons, I noticed the level didn't look right. It was really low. I forgot to close the valve on the pot! The hose was still running to the mash tun and I accidentally dumped probably 4 gallons of cold water into the mash that just got started.
I didn't have an easy way to heat it back up and the LHBS was actually open on Sunday, so I just went a bought new grains, some more water, and started over.
Everything went well until late that night when I was finally finishing. It was really cold. When I went to chill with my CFC, I found that there was no water flow through my garden hose. It was frozen! (so was I) Later, someone mentioned that I should've put it in the washing machine for a bit. Good tip, but instead I was heating up small batches of hot water on the stove and pouring it on the hose until I could get it to flow. This took probably an hour or more to work.
I finally got it chilled and it turned out great, but that was one of the biggest PIA brew days I've ever had.