Every once in awhile I'll be walking along and I will think of something really funny. Something that puts a big fat grin on my face. As I'm vacantly looking around, my face will inadvertently face the direction of some woman. The woman will turn to me and smile. Is this generally an IOI? Are they just being friendly? Is there such a fine line between romantic smiles and courtesy smiles that they are indistinguishable and thus not worth the mental effort we may spend discerning between the two? Would they still smile if I were ugly?