A girl, either ugly, fat, or unpopular, that believes she is a splitting image of Jessica Simpson. Most usually, this girl has a very warped mind about the world, women in general, and mainly herself. She is led to believe due to this disorder that since she is so much like Jessica Simpson, she should be treated as such. If in any case you fail to treat her this way, with all her power, she will attempt to make you conform.
Many believe Jessica Simpson disorder to be related with heavy MTV viewing, cheese intake, and a long/drawn-out menstrual cycle, lasting an entire year. The only known cure is immediate psychiatric treatment. Removal from MTV/Cheese will combat some of the symptoms, but relapse is common.
Currently, 1% of the female population has this disorder, with 10% of those afflicted residing in Wisconsin.
"Dude, just fucking dump Heather already, nobody likes her. She is manipulating you with her Jessica Simpson Disorder."
"I thought the tv remote had a lot cheese powder on it."
"You better wash those hands, she'll lick 'em clean to the bone."