1. When someone starts to message you and write on your facebook wall with the intention of eventually having sex with you.
2. messaging someone on facebook to come over and have sex with you
Guy: "Hey, why would you go after her she's a tramp?"
Other Guy: "That girl didn't mean anything she was just a facebook booty call"
Guy: "Oh that's cool"
Girl: "Why do you keep messaging me on facebook?"
Guy: "Can't you see this is a facebook booty call?"
Girl: "Oh why didn't you say so. i'll be right over"