Peru- especially the Machu Pichu trail. I've heard desperate, poor people will stalk you, then rob you, and won't hesitate to knife you if you don't give them everything. Still going one day anyways, I'll just hire a few local bodyguards :)
Plus Mexico fo sho. I got lost there in a metro station when I was 12. Felt like hours before mum found me. She'd only just finished telling me about a story of a kid in Mexico City who got his eyeballs surgically removed to sell on the black market, then got dumped in a local park. Freaky! I cried like a mothaF.