When someone (usually a guy) won't talk to you to your face but they'll comment on your statuses/pictures, post on your wall, poke you, send you messages, "like" everything you do, and facebook chat you so much that your Facebook account exploes.
Instances of "facebook balls"
Hey, what's up? (wall post or facebook chat)
Hahahahaha (status/picture comment)
Facebook balls refer to the harsh, rude things that people might say on Facebook that they wouldn't say in person.
Rob posted on Facebook that Larry's girlfriend is a total dog. He would have NEVER said that to his face. He's got some big FBB's (Facebook Balls). Then Larry posted back that he was gonna punch Rob in the face. The FBB's must be contagious.