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2.
When you are going down on a girl and you are at the belly button point and is smells funny so u aborth the mission and turn away
(girls name) ask me to go down on her so i started and by the time i was at the belly button it smell nasty so that i had to abort it the misson.

the Belly Button Rule!
by Belly button abort February 09, 2011
 
1.
quite simply, the rule that states if one sees a girl wearing a top which shows her belly button (or more) in public, belly button rule must be declared and girl is labelled slut.
"I can see her belly button with that tiny top on"
"belly button rule, she's a whore"
by wayt00mainstream August 12, 2012