3. He came to the End with me. I spawned back in my bed when exiting, but he didn't (He's probably alive, but lost).
4. I nearly fell into a void, and he ran after me. I flew out, but he didn't.
5. I felt like I didn't want a dog, and soon changed my mind.
6. I was moving into my hotel where I didn't allow dogs, or cats. I killed him and my (newly added) 2 cats.
After my 6th (or so) dog, I finally stuck with cats.
The worst that has happened to me was a while back before they implemented in creative that swords don't break anything.
I made a wooden mansion that took me hours then I built something out of lava on a nearby hilltop. The lava fell straight down the hill onto my mansion.
Forgetting how to make a TNT cannon and trying based on what I remembered.