1. A friend box is the cage you are placed into when you really like someone, but they want to be "just friends". When you have an unrequited love then you are in a friend box.
2. You can also use the term to descibe wanting to be "just friends" with someone.
background: the term friend box was extensively used in the web comic "Dog & Cat" by Tom McHenry during February 2006.
1. guy1: "I've been her friend for six years now, every time she needs a shoulder to cry on, or someone to talk to, or a lift home... i'm always there! why won't she love me?"
guy2: "You can never escape the friend box! never!"
2. guy1: "that girl is so into you, doesn't she get annoying?"
guy2: "not any more, she's been friendboxed, and she knows it."
guy1: *shakes head* "you're such a friend boxer"