I had a dog. This dog was sat down and, wanting to leave the shack of a house I had built out of every type of wood there was, I tried to get it to stand up. I hadn't realized it was right click, and so accidentally punched the dog to death. I was quite sad after that.
Another time within the first month I had the game, I was in creative and had built a rocket ship. Now to add the final detail; fire! I filled the engine up with lava, and watched the lava flow from underneath the spacecraft. I had built it out of wool. Having spent an hour building this, I was--again--fairly sad.