When an unattractive woman believes she is just as dateable as more attractive women based on her higher quality of personality. Said unattractive woman feels that she has been overlooked by men looking for dates, and is therefore bitter towards all men.

Also known as IBS.
Rob: I was trying to talk to that fat chick just to be nice because she looks lonely, but she was a total bitch to me.

Will: Ahh, don't worry about it, she's got a bad case of Inner Beauty Syndrome.
by The Goon Platoon June 18, 2009
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