Most Helpful Guy
You have to be a certain type of guy with a certain type of confidence to be able to do that. It doesn't work for every guy, that's reality. You are asking a girl to form an impression in an instant based on no knowledge of who you are. So if you aren't visually impressive or your confidence doesn't bowl her over then you have no chance.
You have to bear in mind that girls don't necessarily expect or want to get hit on just because they've left the house. They may well not appreciate the approach.