One who always feels the need to be protesting or joining some cause such as greenpeace or PeTA. Causeheads are habitual joiners and often end up abandoning a previous cause for another more promising one.
Protestors who always feel the need to jump from one cause to another or a bunch of causes at once are causeheads.
Individuals who take an issue and stick with it or protest it for about a week; a mob of liberal environmentalists concerned about everything but doing little about it
As you walked around the anti-globalization protest, you could hear the animal rights cause-heads chanting "Save the whales!"