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1.
The common behaviors that often associated with fat girls; however, sometime also occur in fat guys. Some of the behaviors are retarded remark or opinion that nobody cares about, spacing out, moody, and weird annoying laugh when they're alone or without any reason.

Also when a skinny chick thinks that she's fat and starts complaining about her weight and acting all crazy and retarded to the point that you just want to smack her.
Did your girl hung out with her fat ass co-worker again? She's showing sign of fat chick syndrome and it's annoy the shit out of me. You need to get her to stay away from that crazy fat bitch.
by Socal Native August 07, 2011
 
2.
The tendency for overweight females to be surly, moody, nasty and bitchy, thereby rendering them even more unattractive than what they physically are.
"Hey Joe, what's with Michelle? She won't talk to me. I don't care that she's fat and all."

"Mate, it's a classic case of Fat Chick Syndrome."
by Doc Brown August 25, 2009