If you're a guy that doesn't like ugly chicks staring at you, or flirting with you, this one's for you.
If she stares at you, that doesn't mean she likes you. If she flirts, don't be hostile, because she's paying you a huge compliment. If she smiles, make her day and smile back. It takes nothing to have manners. What? Are you afraid if you smile back she'll be misled? Get real! The only time she'll be misled is if you go on to flirt with her, then proceed to ask for her number. If any woman takes an interest in you, simply smile back, if only to acknowledge the compliment.