Human proof design is design that prevents people from successful using the item.
It is similar to mistake proofing except instead of prevent mistakes it prevents people from using it.
When you see human proof design you will often see signs to tell people how to use the device that has been human proofed. Common instances of this are hotels that have shower designs so opaque they need instructions on how to use a device most people have no problem using if they are not human proofed.
Human proof design is often created by a subset of designers that care about how something looks more than how it is used.
Most people prefer designs that are beautiful without being human proofed. The Design of Everyday Things is a great book on designing beautifully with customer focus.
A sign your design is human proofed is that a sign or manual is needed for people to use it.
Most human proof design can be identified very simply by having regular people try to use the item. Watch what they do and when they struggle to use it, many problems will be very obvious. You can’t use people in this effort that are significantly different from the normal users.
In several areas I see these failures quite often. Hotel rooms are a common source of problems. The light switches are often very odd and I have to search all over to find out how to turn on or off different lights.