This one time I was doing a retro in a very high end high rise. The owner swore they remembered the walls from when the place was remodeled, and there was absolutely nothing in the way where I needed to drill. I started drilling and hit something. The owner swore up and down nothing was in the way and told me to keep going. So I kept forcing and forcing until BAM a stream of of water shot out and knocked me off the ladder. I hit the water main, flooded the entire city of Seattle, and caused the governor to declare the entire region a state of disaster.