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 schoolex gfs found me on fatbook last night. Man... she's twice the woman she used to be!"
In an attempt to fatbotage Stephanie, every day at work Marcy left a freshly baked pie on Stephanie's desk, even though she knew Stephanie was on Atkins or some shit like that.