Whenever fat people send you friend requests on facebook, most commonly fat chicks. Also usable when a fat person writes on your wall, or tags you on a status, photo, or video.
Guy 1: Gad Damn it!
Guy 2: whats's up?
Guy 1: This fat chick named carolina keeps trying to add me on facebook
Guy2: oh yeah, yeah i had the same problem with your mom, she kept fatbooking me.
Guy 1: WTF?
Guy 2: whats's up?
Guy 1: This fat chick named carolina keeps trying to add me on facebook
Guy2: oh yeah, yeah i had the same problem with your mom, she kept fatbooking me.
Guy 1: WTF?
by NotRacistCuzMyPresidentIsBlack October 19, 2011
A nick name for "Facebook" derived from users reconnecting with each other after years of no communication and seeing that each other has gained substantial weight.
"One of my high school ex gfs found me on fatbook last night. Man... she's twice the woman she used to be!"
by Dentura Hogfloss April 8, 2009