someone who gawks in your face--inappropriately, of course.
You are on a bus and someone wearing headphones or who looks like they think they're watching a TV program gawks in your face. You don't bother to say "Hello!" (or "WTF?!") because you already know they won't answer nor even blink, but instead you heartily remind yourself under your breathe, "(It's just) a brain-dead gawker (oh yeah!)"