Someone who plays their guitar very high, so that the headstock of their guitar is at the same altitude as their nipple.
Although they are often teased by the faggoty emo/metal junkies, Nipple Riders are the only ones who can actually play a note properly.
Moral of the story: don't sacrifice tone just to look "cool".
Emo kid: Eww look at that Nipple Rider!
Person: At least he's not a dick rider.
Emo kid: .... touche.
Girl: Whoa, you look and play guitar like a fucking g. I offer my pussy to you.
Nipple Rider: kthnx.