I did a study of a women on the train and then she looked at me from five rows infront/away and i held up the drawing pad to show her and she gave me this look as if i just tried to rape her mom!!!
Hahaha. Well, most people don't react too nicely to being drawn without their permission, I've noticed. The best is when they're in a situation when it would be socially unacceptable to call attention to it, like a classroom. Then they have to sit there and stew in discomfort.
Stick to drawing pictures of your friends, if you want to show your subject your work. Otherwise, keep secretly stealing people's souls from a distance.