During Brian's game of Field of Fire, before Law shows up, Brian goes AFK to take care of his cat. Said cat begins to attack him. The people he's playing with can hear him through his microphone. Their perplexed reactions to lines of dialogue such as "GET OFF CHEETO" are priceless.
Even better is when Law walks up to Brian, just as the latter says yet another It Makes Sense in Context line. Law's "What the hell?" face is the best.
Brian: Mom! Where's the iodine?
Law: ...whatever, kid.
Another great part of that gag is how the lines were given through a vacant expression. Sure, it's probably just a clever audio/video sync, but it's still funny.
Brianpalooza. That is all.
Law suddenly gaining a Badass Mustache out of nowhere in episode 4. He then keeps it for the rest of the episode.
Jenny: What is this? Is this going to be a thing, now? Law: What? Do you (points to his shirt, which says) "like my stache?"
Ace: Rule Number 271: Never quote my rules back at me. Now sit your punk ass down and best of luck to you, son.
Also in Episode Nine, The Law's reaction to Jenny pulling her gun on him when he breaks into the game:
The Law:(in a high pitched voice) Awkward!
In season 2, Ki has just read a complaint in the RA box. At the end it is signed by The Law. Just as she reaches that part, The Law knocks the letter out of her hands, screaming, "THE LAW!" Before loping away, arms touching the ground, like a monkey and shouting "I just did that!" to a passing student, implying that the narration of the letter we heard in the Law's voice was actually him reciting it as Ki read it.
Every single scene featuring The Law in Episode 2 is this.
Season 2, episode 3: Brian is serving a brunch with Calhoun, Jenny, Jenny's mother and "The Baroness." The Baroness orders everyone tuna, and as Brian leans towards Calhoun to apologize for being late, Calhoun looks up at him, utter terror in his eyes, and whispers:
Calhoun:I'm allergic to tuna!
Later see saw Calhoun being taken to the hospital, all but confirming he had to eat the dish.
Season 2, episode 4 ending: The Law is preparing to confront a potential enemy in a dramatic entrance... only for him to kick in the next door over, interrupting... whatever the student was doing. He apologizes and makes small talk before moving on. Made even better that the potential enemy can hear all of this muffled through the wall.
Another one from that episode has to be the sheer beauty of Cheeto sailing through the air and coming to land on Brian's face.
Season 2, Episode 6, the Law is called in to a playoff game, and as he triumphantly walks up to the table, music swelling, he throws up. Three times. Topped with his remark to Brian:
Law: I'm probably gonna throw up again.
Brian leaning away from him after that line just adds to hilarity.
The Behind-the-Scenes videos have many wonderful moments, but Season 2's ending moment has particularly wonderful multiple takes of Law's exit from VGHS with the different lines being approximate to, "let's blow this taco stand":
The Law: Let's hang glide out of this loser emporium.
[the cast and crew crumble into fits of laughter]
When Jenny has an interview with OMG, the Talkbot asks her to rank her favorite races. Unfortunately, Jenny interprets this as actual human races.
Jenny: Well, I guess that...I'm white, so white. And then I love Indian food, so maybe that would be two.
Talkbot: ...We were talking about World of Warcraft.
Ted: Use the breath mint! It's gonna boost your confidence!
Brian: Guys, I can kiss Jenny on my own, okay? Trust me.
Cut to Jenny, who suddenly appeared at the door.
Jenny: What now?
Brian: RAAAHH! (throws game away)
Near the start of season 3 episode 2, Law ends up having to do a trust fall with Shane, and everyone's egging him on to do it. He's reluctant until he sees his girlfriend outside yelling "DO IT!" from the car that he arrived in.
When Ki is investigating a case about Cheeto (who's gone missing), she meets up with Games. Unfortunately, she was wearing high heels, so while advancing towards him, we see her awkwardly stumble, having to use the doorway to support herself.
When Brian and Games' crew gets caught in their acts by two cops and end up in a police station, Brian is asked if he has anyone to call. Cut to Calhoun driving Brian back to school.
Calhoun: God, I hate my job.
When Ted's playing an arcade game called Wave Race, a fantasy of his is shown where he rides a jet ski naked while shooting a gun wildly.
In season 2 episode 5, the Shotbot is saved from deactivation by Scott, and the latter tells the former to go run and find a "human story". Shotbot does so while wearing a Paper-Thin Disguise to look like a female student. What's even more hilarious is that everyone actually falls for it, and he actually becomes the Law's girlfriend.
Even more amusing is the sheer disbelief that Shane expresses when the Law tells her that Shotbot is his girlfriend.