Why would you want dirty hair? I don't know, maybe because my clean hair is flat and boring. Perfectly dirty hair is never oily. It's dry, kind of wild, and gritty -- the base for a great hair day.
I've been trying to last longer between washes, and now I'm down to only washing my hair twice a week. (And I run!) On days that I do wash, I mimic the dirrrrty hair with this salt spray.
(All of this must sound like crazy talk to guys.)