As I said in your other questions, I don't like words like hot and sexy. I don't feel like those are words you should use to describe a woman. Still, even if I saw someone I thought was beautiful, I doubt I would come up to her and say so. I rarely think any girl as physically good looking enough to be called beautiful without knowing her, so if she was, I think I would be rather quite nervous to try and talk to her, not to mention she would probably get complimented all the time anyways.
But I apologize for being off-topic. What makes a person beautiful? A combination of who you are on the inside and outside. The combination of everything about you that makes you unique. Their little quirks. Their scars, both physically and mentally. Their personality, and how it reflects in the way they act, their voice, their facial expressions, their eyes. How you can't see how truly beautiful someone is, until you know them well.