A person who is headie
or a head
(ie into the jamband scene) and believes they are better than other fans because they have been to a large number of shows, tour extensively, know a great deal of statistics by heart, wear a lot of patchwork, or are extensively organic--anything to do with the jamband scene. Essentially a jamband snob.
Just as “holier-than-thou,” is a word one would use to describe someone who believes they are better than others for their moral points of view, the person who is “headier-than-thou” thinks s/he is better than other fans because of their level of “fan-ness,” or at least this is what other heads believe the “headier-than-thou” person is communicating through their behavior.
That guy won't shut up about how many Phish shows he's been to. He is so "headier-than-thou."