Handicapped parking is the subject of little discussion anymore. You either have a permit to use it, don’t have a permit to use it or you’re just waiting for someone inside a store and you’re not parking, you’re just standing (and you’re an asshole).
It’s pretty cut and dry who should use handicapped parking (the handicapped). Handicapped bathroom stalls are a whole different situation and nobody is really sure how the ethics work.
First, a definition. Businesses are required, by law, to provide a handicapped bathroom or bathroom stall. These are wide enough to accommodate wheelchairs (of other assistance devices) and include handles and other details to make bathroom time easier for the handicapped.
Unlike parking spots, there isn’t a restriction on using them. Some businesses only offer one bathroom that happens to be handicapped accessible. Others have specific bathrooms. Most commonly there are full bathrooms with a designated stall. They’re free game to the handicapped and able-bodied population. There are a few different opinions though on when you can use them.