The Incest Rule, also known as Rule 999, requires you to have sex with your close relatives at any time possible.
"My cousin is coming over tomorrow."
"The Incest Rule?"
"You're dead to me."
When given the opportunity, you are obliged to engage in sexual intercourse with all nearby cheese graters.
"Wow, cheese graters!"
"Rule 540, man. Rule 540."
"Dammit, Bryan!"
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