Falling through the ceiling
Well, I was up in the attic, installing an attic fan. While walking across the joists, I slipped on some insulation and put my foot through the drywall of the ceiling below. While falling, my other foot slipped and pushed through a different ceiling, so I ended up straddling a wall.
Instinctively, I flopped and flailed my arms to catch ahold of something in case I went all the way through. I ended up flat on my back with my legs hanging out of the ceiling. My dad came up and said “Uh, are you all right?”
“I’m fine. I just can’t believe I did that!”
This is the hole on the hallway side of the wall:

This is the bathroom side:

… and this is all of the insulation that fell out of the attic.

All in all, this could have been much worse. I’m okay and the damage isn’t too bad, so now feel free to laugh at me in the comments.
Oh, and never work in the attic if you don’t have someone around to help if you have an accident.
