Okay kiddo, imagine your body is a machine and it has different parts that need to work together in order to function properly. Sometimes, some of these parts stop working because you don't use them enough. This is called disuse.
Disuse supersensitivity is when your body reacts to this lack of use by making the other parts work even harder. It's like if you were playing a game with one hand tied behind your back- you would probably use your other hand more to compensate.
In the same way, if one part of your body is not being used enough, your body will try to make up for it by making other parts of your body more sensitive to certain things. This can happen with things like drugs or even simple things like touch.
So basically, disuse supersensitivity is your body trying to do the best it can with what it has when some parts are not being used properly.