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1.
Always carry a knife

(originated from S.A. Gibbs' unwritten list of Rules, as per NCIS)
AGENT: Thank god for Rule 9! Now I can cut off these ropes!
by MissNoodles June 23, 2006
 
2.
There is no rule 11
Guy:..... Wait where is rule 11?
Guy 2: Rule 9
by Dr. Crowley January 23, 2010