I'm a bit old (42) so back in the day being rejected was not a big deal since you had to approach the girl on the spot 99% of the time (club, street, party or whatever). Just the way things work. You just move on. If we're talking about a girl that's in your social circle that rejects you, never give her a second chance. You can have some sweet moments with her when she changes her mind, but nothing more than that. The reason: it's her vanity 99% of the time, she doesn't suddenly start to like you, she just wants to see if you'd still fall for her. The best thing is to move on to someone who really likes you from the get-go.