When I was a graduate student at Berkeley in the 1990s, the philosophy graduate student lounge had a billboard on which we posted philosophical humor. (Leo Van Munching, bless him, kept it organized; there never was, by the way, a more beautiful unpublished philosophical prose stylist.) Among the items that lived a span upon that board was a newspaper clipping in which a French coiffeur claims not to be a barber but rather "a philosopher of hair". Part of the humor in this, presumably, derives from the strange idea of a philosophy of hair. (Another part of the humor comes from its playing upon the different perceptions of philosophy in France and the U.S.)
But why not a philosophy of hair? It seems to me the following are recognizably philosophical questions:
(1.) What distinguishes a haircut from other events in which one's hair ends up shorter (e.g., fire, lawnmower accident)?
(2.) Is a good haircut timelessly good, or does the quality of a haircut depend in part on the tides of fashion?
(3.) Must a haircut please its bearer to be good? Are there, perhaps, several different dimensions of "goodness" to be pulled apart here?
(4.) To what extent should a haircut be judged by the intent of the hairdresser?
Now maybe these aren't earthshakingly important philosophical questions; but they do bear a certain resemblance to philosophical questions in other branches of philosophy (especially aesthetics). Yet they aren't merely derivative of those other questions: One's answers probably need to involve factors particular to hair. They can't simply and straightforwardly be derived from one's general stances about authorial intent, the quality of works of art, etc. And I don't doubt that our French coiffeur would have opinions on all of them!
Why do I care whether there is a philosophy of hair? Here's why. If there is, it suggests that philosophy is not a subject area. It is an approach, a style of thinking, a willingness to plunge in and consider the deepest onotological, normative, conceptual, and broadly theoretical questions regarding anything. Any topic -- the mind, language, physics, ethics, hair, Barbie dolls, carpentry, auto racing -- can be approached philosophically. For all X, there is a philosophy of X. Ain't that grand?
Consequently, when people say "this is my philosophy of X", I think they are generally using the word "philosophy" quite correctly. We should not cringe. John Madden is a philosopher of football!