re: overly polite folks at 4-way stops
if they wave me through, i'll go. if not, i'll give the head nod indicating they should go. that seems to work well.
re: riding to stone mountain
i'm female and the closest thing to something shady i've seen was a dude riding circles in the street around decatur yelling at things only in his mind. my commute is through east atlanta, reynoldstown, old 4th ward, downtown, midtown and i haven't had any problems. in a city you should always be aware of your surroundings on the bike or not. if you keep scanning what's going on around you, it's hard for someone to sneak up on you.