in my bathroom
(hereinafter to be referred to as TMTFH: The Mystery Toilet From Hell) once refused to stop running. As a result of messing with its innards, the tank refill valve blew apart into several pieces, with the water on.
Now I was presented with an interesting situation; water shot straight out of the bared valve stem and hit the ceiling, until I covered it with my hand. If I covered the little geyser with my hand, I could not reach the shutoff valve on the wall with my other hand. Finally, I just plopped the lid back on the tank, and tried the shutoff... which revealed itself to be permanently corroded in the on position.
I went outside and tried the shutoff valve at the side of the house... well, almost tried it, before I realized it was guarded by a HUGE nest of yellow jacket wasps. I found a shutoff valve attached to the water meter, but it would not turn by hand, so I ran in to find a pair of pliers. It was only after that when I discovered that the drain was clogged somewhere downstream of the toilet, and three rooms of the house were starting to look like indoor swampland...