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

Rule #12

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

Tony: So he pulls me into his office and I think he's going to chew me out for that thing I said about his hair, right? But no. He wants to know if I think he's being doing an okay job.
McGee: The deputy is no Director Vance, that's for sure.

Tony: I've heard the saying "he got blown out of his shoes", but I never thought I'd see it.
Ducky: Now if the explosion had knocked his socks off, that would be impressive, wouldn't it?

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

Never be unreachable. (Season 3, Episode 13, Gibbs)

Rule #3

NCIS Quotes

Bishop: Seriously? How'd you get that?
Tony: Well, it's like Gorillas in the Midst. You'll get to understand his grunts.

Torres: When I break out the glass, maybe I can rip out the bars.
Bishop: With what? Your superhuman strength?