Specifically - intergluteal cleft hair...... Surprisingly, not much research has been put into that, but - some people really want to know it seems... And there are theories about it, after all. Theories that are mainly in line with those about armpit hair, but still. Now we have an answer! (Slightly NSFW? For drawn butts and PG rated butt related language? I really don’t know what SFW with you guys over the pond, so... :) )