What kind of idiot closes all the bathrooms because of graffiti? Oh, that's right, it's Maryland Massachusetts California!
Some Maryland High schools were locking bathrooms in the '70s during 'racial unrest'. The only problem was that the locks could be controlled without a key from the inside, and you had to have a key to get in from the outside.
Whatever was going to happen inside happened, be it smoking cigarettes, fights, whatever, and when the key was finally produced, chances were that everyone had left the room (or the building via windows) anyway.
The idea was stupid then, it is only more so now.