Robert Fuller, author of Somebodies and Nobodies and All Rise, has coined a great term: rankism. He says rankism is the mother of all isms - sexism, racism and so on, because at the other of all isms lies a power advantage that one has over another. Of course, it's not power that's the problem, but abuses of power.
Obviously, some people use colour or gender (or whatever it is) to outline their claim of supremacy over others - but lying at the heart of all this is the issue of power.
Viewed in this context, all abuses of power - eg a doctor abusing a nurse, a professor exploiting a graduate student or a boss bullying a subordinate qualify as forms of rankism.
(email me your comments at firstname.lastname@example.org)