Lot of great suggestions here. I'll throw one in that has seemed to work for me between ages 17-now 26 years old. ALWAYS have resting bitch face or looked pissed off. I cannot say this is the single variable that has helped deter creeps from talking to me, but I have yet to be approached because I always try to come off as unapproachable as possible. Not many men like a shrew, unless you're Heath Ledger from 10 Things I Hate About You. I also emphasize saving Metro PD's number 696-873, so she can text for help.