Bend the line, don't break it. (Season 11, Episode 4)

Rule #14

Never, ever involve a lawyer. (Season 6, Episode 7; Gibbs is said to have other rules involving lawyers, but according to Tony, this is the "umbrella" one)

Rule #13

Never date a coworker. (Season 1, Episode 15, and referenced on other occasions)

Rule #12

When the job is done, walk away. (Season 6, Episode 24)

Rule #11

Never get personally involved on a case. (Season 7, Episode 21)

Rule #10

Never go anywhere without a knife. (Season 1, Episode 13)

Rule #9

Never assume. (Season 9, Episode 21)

Rule #8

Never take anything for granted. (Season 3, Episode 10)

Rule #8

Always be specific when you lie. (Season 1, Episode 23)

Rule #7

Never apologize. (Season 7, Episode 12, but referenced previous times without a number attached)

Rule #6

You don't waste good. (Season 8, Episode 22)

Rule #5

The best way to keep a secret? Keep it to yourself. Second best? Tell one other person, if you must. There is no third best. (Season 4, Episode 11)

Rule #4

NCIS Quotes

McGee: Rule number 70 - keep digging till you hit bottom.
Abby: McGee! There is no rule 70.
McGee: Well, I--
Abby: You just made up a rule. This McGibbs thing has really gone to your head. I don't even recognize you right now.

[voiceover] Anyone can achieve their fullest potential, who we are might be predetermined, but the path we follow is always of our own choosing. We should never allow our fears or the expectations of others to set the frontiers of our destiny. Your destiny can't be changed but, it can be challenged. Every man is born as many men and dies as a single one.

McGee