i'd like to share my opinion on this not because i'm a skilled martial artist but because i was a human punching bag from the 3rd grade to my senior year in high school. still though, i picked up some useful strategies.
- If someone's staring you down, don't look away and ignore it: it's the #1 sign of fear. "oh i wish you would just stop looking at me," is what you're telling them. someone else here mentioned looking confident, and they're right: look back at them, nod with a blank, confident look on your face, maintain posture, and walk straight ahead without looking down. don't be a tough guy, just be a guy that's proud to be who he is.
- if they taunt you, or call for your attention, don't ignore it: again, it's a sign of weakness. look straight at them and say something like, "sorry, gotta go" or something along those lines. my point is that as long as you say something back to them, you show them that you're not afraid, but you're not being aggressive either. just say anything, as long as it's innocent, and say it with confidence.
of course, this is all high school theatrics. if i was in a sketchy area, and someone looked at me, i wouldn't dare look back. i'd rather look weak than be dead.
i passed a group of guys up in Boston that ended up mugging me. it was my fault; i shouldn't have looked down and ignored them. i would've gotten a good look at their faces, which would discourage them from attacking me, and i showed weakness which would only encourage them more.