Never leave behind loose ends. (Season 3, Episode 24)

Rule #45

Clean up your own mess. (Season 7, Episode 24)

Rule #45

First things first. Hide the women and children. (Season 7, Episode 23)

Rule #44

Never accept an apology from someone who just sucker punched you. (Season 9, Episode 16)

Rule #42

If it seems someone is out to get you, they are. (Season 7, Episode 22)

Rule #40

There is no such thing as a small world. (Season 10, Episode 14)

Rule #39A

There is no such thing as coincidence. (Season 7, Episode 21)

Rule #39

Your case, your lead. (Season 6, Episode 16; Season 10, Episode 3)

Rule #38

If feels like you're being played, you probably are. (Season 9, Episode 1)

Rule #36

Always watch the watchers. (Season 8, Episode 22)

Rule #35

Rule #27: Two ways to follow: First way, they never notice you, Second way, they only notice you. (Season 7, Episode 15)

Never mess with a Marine's coffee if you want to live. (Season 2, Episode 9)

Rule #23

NCIS Quotes

McGee: All right. Well you should probably know that Abby and I used to date?
Bishop: Ew. Like, each other?
McGee: Yeah.
Bishop: Wait - isn't that a violation of rule 12, never date a....
McGee: It was a long time ago. After we'd broken up, one night I went to her lab. Found a scribbled piece paper; a list. Potential boyfriends had to fulfill certain conditions by a pre-arranged date or else, goodbye.
Bishop: Such as.
McGee: Things started off relatively normal: opening the door for her, flowers, putting the seat down. Then around number 8, it gets uh...
Bishop: What?
McGee: Does she know you have these?
Bishop: Does she know you have these?
McGee: Yeah she wasn't happy when she found out.
Bishop: These are all very specific.
McGee: Yeah.
Bishop: These ideas apply to you?
McGee: No those rules weren't in place when we were together. At least I don't think so.
Bishop: What's with the two month cutoff? Abby's sabotaging herself. I've seen stuff like this before. We have to talk to her.

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.