I think that the worst feeling in the world, is that feeling when you get in the shower and turn on the tap, only to realize that you forgot to turn off the showerhead the previous day.
That split-second of dread, and realizing what’s about to happen is probably even worse than the impending blast of ice-cold water that arrives soon afterward. It’s just enough time to look up and say “aw, fudge” dramatically, but not quite enough time to leap out of the way.