Deadpan Snarker: To give just one example, Callen and Hetty are in a graveyard remembering the dead. Hetty remarks she wants to just be gone: no flowers on the grave, etc. Callen says it won't happen, because he hears Granger's going to have her stuffed.
Feuding Families: The almost 70 year old feud between Callen's family and the Comescu family is the reason why he is an orphan.
Last Name Basis: At one point, Callen asks Hetty why she never calls him by his first name (though she usually calls most of the other agents by their last names, too). She responds, "It's not a name. It's a letter."
Last of His Kind: Callen is apparently the only living member of his family, which a certain Eastern European crime family has been hellbent on wiping out.
Omniglot: G can speak English, Arabic, French, German (Which some people says has an Austrian accent), Italian (With a Northern accent), Polish, Russian and Spanish. He says that he can speak Czech and Romanian. In "Allegiance", he can speak Turkish. But Sam chews him out for not speaking the right words.
One-Letter Name: Due to the paperwork with his full name on it getting lost by the foster system.
Cunning Linguist: If there's a foreign language the team needs, Sam probably has it.
Genius Bruiser: A former Navy SEAL and all around Scary Black Man. As previously mentioned he speaks three additional languages fluently and can handle himself in Farsi, and he has extensively studied sharia law and the Qur'an. Justified: They don't let Dumb Muscle into the SEALs.
Happily Married: Although it isn't brought up much, to the point where Kensi and Deeks were very surprised when he offhandedly brought it up while interrogating a suspect. Callen knew about them, though.
Omniglot: Sam speaks native English with Arabic, Japanese and Spanish. He's familiar with Farsi, but he didn't speak the language for a long time. In "Allegiance", he can speak Korean. But G chews him out for not speaking the right words.
Parental Abandonment: At least to his kids. The only thing Sam doesn't like is that extended hours makes him miss out on his kids' lives like school graduation.
Scary Black Man: He uses his height and musculature to intimidate when he's working or using an alias, and even with his coworkers, he carries a strong aura of "Do NOT mess with me."
"Anybody want to put a leash on him before we go another round right here?"
Eye Scream: To a degree. Kensi - and, of course, the actress - has an unusual birthmark on the white of one of her eyes which gives her a distinctive look. Viewers who might not be aware of this unusual trait might think that Kensi, or the actress, has some sort of eye injury or a completely dark eyeball depending on the lighting and camera angle. In reality, of course, neither is the case.
Friendly Sniper: She enjoys the usual camaraderie with her colleagues, has an "are they or aren't they" relationship with another agent, and often takes part in the show's humor. And the in the next scene she is cold-bloodedly sniping bad guys to death. She doesn't fit the "loner" aspect of the trope, but otherwise ... shudder.
Lad-ette: Views of her home are basically that of a bachelor pad.
Ms. Fanservice: Perhaps the inevitable result of being the only female regular under the age of 40 (until Nell came along, but Nell's not that sort of character), although she's fairly mild compared with some - but a lot stronger than Ziva David.
Omniglot: She can speak English with Portuguese and Spanish. (In real life, Daniela can speak the last two languages fluently aside from English, which doubles as a The Cast Showoff). In "The Dragon and the Fairy", she displays her proficiency in French.
All Take and No Give: Despite his Butt Monkey tendencies, he would probably be this wasn't it for casual hints from the team that they do care... which become increasingly less casual.
Ascended Extra: Got promoted from recurring character to principal cast in season 2.
Berserk Button: A dirty cop once mocked a woman Deeks had a relationship with; a fellow cop that the dirty one had framed for his activities after she'd been killed by a crimelord. Deeks pulled his gun on the man, and after surrendering it to Sam, proceeded to beat the hell out of him with his bare hands.
Butt Monkey: As the newest on the team, G, Sam and his partner Kensi all tend to pick on him, though he tends to either shrug it off or play it up. In one or two tense episodes, it's implied he sets himself up for teasing to lighten the mood.
Distressed Dude: After being shot twice, kidnapped, used as bait, beat up on numerous occasions, and being involved in more explosions than this troper can count - honestly, the only person who MIGHT rival him is Callen, and that's only because he's the last surviving member of a family that's been feuding with another for decades and everybody wants to kill him.
Though he may count, at times, as a Badass in Distress since he does tend to get himself out of those messes.
Considering he saved Kensi's life by shooting the baddie before he could kidnap her after racing down a couple flights of stairs to get to her when he worked it out in his head that he was the bait to lure her out of hiding. And that was after he'd been shot. Twice.
Drama Queen: He is always freaking out in the worst times. Normally used for comical relief.
Non-Action Guy: The one time he's forced into the field, he's terrified he'll have to carry a gun. Hetty gently informs him she wouldn't forgive herself for forcing him to carry a weapon, and he's happy to return to Ops when he's done.
Preppy Name: He gives his full name as "Eric Bartholomew Beale III, Esq." in S 6 E 2, "Inelegant Heart".
Belligerent Sexual Tension: She and Eric lapse into this when she feels he doesn't give her enough attention, or when they become slightly competitive. It is mostly playful and benign.
Beware the Nice Ones: Unlike Eric, she is field trained and carries a gun when in the field. She hasn't had to use it that often, but she has captured a few suspects and disarmed a trained opponent who had taken her hostage and was using her as a human shield.
Xanatos Speed Chess: In the Season 5 premier, during his escape from Callen, Marcel constantly updates his strategy to the point of cutting off parts of his own skin just to get rid of the tracking residue Callen placed on him.