When you know a girl who is currently in a relationship and you know that relationship won't last so you stay in touch as best you can with the girl in hopes of scoring a rebound when she breaks up. Can be done with multiple girls as well.
Tom: Hey John I noticed you are staying in touch with Chelesea and Brittney lately. You two good friends?
John: Nah dude they are both in relationships which I know they can't keep. As soon as one of them breaks up I'm going in for the kill.
Tom: Fuckin' cherry picking