A phrase/ mental disorder which discribes the social immaturity displayed by women(ages 14-19) with flat chest. It's usually diagnosed by a friend or first time aqaintance who notices certain idiosynchrasies that display annoyance, or in gereral over compensation.

Victims of FCS often display narcissism, or self-centeredness; They often try to compensate by trying to be intellectually superior or catty.

It's often grown out of but the long term effects can only heal with time.
Abel- Dude (girl) is being so annoying
Chelsea- Yeah I know she must have Flat Chest Syndrome(FCS)
Abel- Oh yeah she's deffanently FCS positive.
by Chabel Roeschstraviz March 27, 2008
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