Top definition
Sperm Build-up Theory: A girl with a really nice ass, starts dating some guy who is clearly tagging her, and her ass gets much larger, while everything else stays proportionate.
Jessica follows the S-B theory to a tee! She used to be smokin', but since she started dating Mark her ass has become huge! Must be sperm build-up!
by JMSMD September 24, 2006
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