Not just any bookcase will fit your head. That's why this one is custom made. Darragh Casey's Shelving the Body project requires users to stay shelved along with their belongings or else they'll fall down:
Rather than creating generalist shelves that support all nature of goods, he began experimenting and creating shelves which rely on people to use their own bodies and weigh to support or counterbalance objects or require users to carefully configure their objects on the shelves. Some shelves require the user to take a certain position and in his shelving the body project, shelves are designed to support human bodies themselves!
Link and Artist's Website -via Bookshelf
This guy seems to have drawn round his mates and nailed some planks to the wall.
Thats the difference for me between those two examples anyway. Obviously its always subjective.
This site does get it right much more often than it gets it wrong, if you play it safe, you might miss something great. It can be good to see something pointless to put things in perspective too so I say your doing a good job.
I often post offbeat works of art, frequently with great success. This piece, for example, did pretty well. Can you offer any specific criteria for distinguishing between the artistic and the banal?