BBF
"Back up Boy Friend"

As in the guy you would like to date if something happens to your current boyfriend/crush. This is sort of like insurance if your old boyfriend breaks up with you. (The guy used for your rebound)
Girl: "I don't care if he dumps me I've still got my BBF."

Friend: "Not anymore, I heard he's dating Shelby."

Girl: "Ahh! I need a new BBF!"