haha, i have the same issue. I just look straight but look confident. I don't even make eye contact with them.
I always say Hi and smile or comment on how freakin hot it is outside or compliment something even if its not worth complimenting when on the inside I'm boiling cuz I'm so mad that they felt the need to stare me down. Someone just passing by and glancing at you then looking away is fine and I'll just look straight ahead but someone staring at you the whole time as you pass them feels like they're insulting you w/ their eyes or trying to feel bigger than you by seeing if you'll look down or away first. I think its just my own complex, I'm a petite girl and some ppl seem to think small girls are always shy and don't like confrontations therefore you can insult them or belittle them whenever you want. Most ppl look straight ahead but occasionally women will look me up and down and just give me that "ugh" look. I'll look behind me (make sure its not someone else they're talking about) wave and walk a little faster towards them "Oh! I saw you staring at me I thought you were someone else, sorry ya'll have a good day!" or warn them about some non-existent crazy homeless guy who might try to grope them around the corner.
I look straight ahead. I smile only to people I know.
For some unknown reason, I smile at babies, tots and very old people. Most of them smile in return (mostly the elders).
I find people staring at me, then i look away thing about what i look like...