A few years back, I needed to go badly over at a friend's place. His toilet wouldn't flush properly, so I got my friend to help fix it (since I've never used his bathroom before, don't know where everything is). He proceeds to try and flush the already-near-overflowing toilet again, and it all spills onto the floor, and leaks into the carpeted hallway.

They had to remove the carpet and replace it with hardwood flooring. Poor family.