Top Definition
A Thereom that details cases of super-nerdy teenaged guys that have freakishly hot sisters, the kind that you wonder: "How the hell does that come from the same thing that made that!?"

The sister in question usually becomes wicked-hot during puberty in a ugly-duckling to swan transformation, while the brother goes through a ugly-duckling to ugly-duck trnasformation.
Guy1: "Look man, it's Eugene and......Liz?"

Guy2: "OMFG bro, how the hell did Eugene and Liz come from the same vagina? Liz is the hottest piece of ass since Megan Fox."

Guy1: "Dude, I know! But according to the Anderspn-Best Thereom, every nerdy fag has a mega-hot sister."

Guy2: "Thank God for the Anderson-Best Thereom!" *high fives all around*
by TheSandman321 September 07, 2010

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