I appreciate this thread which got me back into the aspect of asking at time for some variety in shots.I got over it when I got into the car show/tuner scene, would go to a show, shoot all the hired models, then start asking the attractive female attendees. They loved it cause of attention from us show photographers, a few of them turned into model shoots down the road. Their boyfriends were geeked too. Fairs and festivals were great to do it especially if you have business cards and you are trying to make new contacts.
For the most part, I don't I ask people for permission to take their photos when I do street photography.