Its shit if the girl doesn't have any sexual interest in you, you jut inflate her ego. Some girls will send out signals with body-lanuage to lure guys in. They stare in certain way flip their hair walk by you certain way then when you give attention its get away you loser.Flirting is best when the girl gives signs she is into you,there is a small ass window, you have to sexually escalate.
It's when you start talking to a girl in the same way to talking to a guy friend. You tease them and mess around with them, while still talking to her like you actually enjoy talking to her as a person.
It's really easy to just try out on subhuman looking girls since the cost/benefit is good. Once you get the hang of it, you'll be able to see which girls are immediately disgusted by you and which ones aren't by flirting with them.