This is the standard shower control in many gyms and hotels:

This is about the worst controller their ever could be. A simple person might look at this and think, hmm… the big pointy thing is pointing to hot. It must be very hot! No, simple person, this setting means “Off.: This shower is so special, its pointer does not work like every other big pointer in the entire world that points towards something. No, this pointer, points away! It is not like a clock, or a highway exit sign, or a mouse pointer, or a one way sign. It is special! Why? I haven’t the least idea.

Oh, and for a bonus there is no way to adjust water pressure.