I have a few:
I was acclimating an orange GloFish when he managed to jump out of the bowl, which was at least a 2" jump. I came back into the room to check on him and he wasn't in the bowl so I freaked out. I couldn't find him anywhere on my desk, where the bowl was, I found him on the floor, which was about 6 feet below. He made it through, though. The next time I was acclimating an orange fish, it jumped out of the bowl too, almost the exact same situation, except this one didn't fall on the floor. That fish, Torpedo, is still alive today. I've developed a theory that orange fish are naturally suicidal.
Back before I knew better and I was keeping a GloFish in a bowl, I was using glass rocks as substrate. Well, one day I look in the bowl and I can't find Twinkle. I look around the tank and I don't find anything, so I looked in through the top of the bowl and saw just her eye looking up at me from underneath the glass beads, "HELP ME!" I don't know why she decided to go digging but she got stuck. She made it out of that alive, though, and she also made it through me learning how to set up a real fish tank, too.
Then in my SW
tank, I use an overflow cup on my display tank, which goes down to my sump, etc. Well I have a small yellow clown goby in there named Sunny, who was one inch long at the most. I couldn't find him for a week or so (plenty of places to hide) but I assumed he died or got eaten or something. Well one day I look at the back of the overflow cup and I see him sitting in there, next to a sponge I had in there. I couldn't shut the pump off because then the water would run out of that part of the overflow, and I couldn't remove most of the stuff in there or else I'd risk him going down the pipes and into the mechanical filtration, where I don't think he'd make it. It was interesting getting him out of there, but he made it. He managed to get back there again before I blocked that off, which gave me yet another ulcer. He's fine, though, and he's stil alive and doing fine in my SW