Isaac Lahey is one of the fan-favorite characters of Teen Wolf, even though he's only on the show for a few seasons. He's a unique character who adds a lot of humor to the show, but he also has a very moving and well-rounded arc. Perhaps, like Stiles, sarcasm is a defense mechanism for him.
Isaac comes from a troubled background, so it takes him a while to confirm his alliance with Scott. When he finally does, not everyone is willing to accept him in the pack. He wins over their trust by proving his loyalty and making awkward jokes - which is where most of his memorable quotes come from.
"I Guess This Is The Part Where I Say Something Witty ... I'm Not Witty."
During one of his fight sequences, Isaac takes a moment to soak up the feeling of winning. Before finishing off his enemy, he pauses, his weapon slung over his back, and looks down at his captive. Isaac pokes fun at the cinematic stereotype of heroes who deliver poignant speeches or memorable remarks right before killing a bad guy or doing something heroic.
"I guess this is the part where I say something witty," Isaac says, then pauses to think before finishing, "I'm not witty." The scene cuts away as he lifts his weapon so that viewers only remember his humorous remark. Isaac often says things matter-of-factly, knowing he's funny, but not caring if other people laugh or not. Usually, Stiles is the one to rein in his ego, but this is probably because he feels threatened by Isaac's presence in Scott's life, as well as his uncannily similar sense of humor and general personality.
"Yeah, I Can Still Hear You - Very, Very Clearly."
In season 3, Isaac is helping Scott and the others with an elaborate plan to capture the twins. He's in the car on a video call to Allison's phone. His cue to action is the twins' appearance in the video. While setting up the call, Allison asks him if he's nervous. "Do I look nervous?" he asks, and Allison reassures him that he doesn't.
In the background is Chris, who asks Allison if he really did look nervous. "Terrified," she confirms, but Isaac says he can still hear them. Like a typical teenager on Teen Wolf, Isaac tries to defuse the tension with humor, but it's obvious that he's concerned about the task ahead.
"Well, I'm A Little Bummed At Being A Fugitive, But Other Than That, I'm Great."
When Derek is rushing to build up a pack in season 3, Scott worries that he isn't using the best method of recruitment. He confronts Derek while Erica, Boyd, and Isaac are training with him, but Derek uses this as an opportunity to beat Scott down. He's still not over the fact that Scott has his own pack, and he wants to prove that he's more powerful.
He asks Erica and Isaac how they're feeling, to which Isaac responds with the quote above. After being bitten by Derek, he was falsely accused of his father's death, so Derek and Scott had to break him out of jail during his first full moon. Isaac may have a lighthearted response to Derek's question, but he will soon realize that he's better off with Scott, whose motives are purer. Similarly, Erica and Boyd end up as two of the saddest deaths in Teen Wolf, and Derek's desperation for power is partly to blame.
"Yeah, Well, He Doesn't Trust You, Either."
Before Isaac becomes one of the main characters of the show, Scott and his friends are wary of him. Not only does he behave a little strangely, but nobody really knows anything about him. This is largely because Isaac has a dark past that he doesn't want to talk about.
So, when Derek brings Isaac with him to help Scott track down the kanima, it's no wonder Scott is confused. Derek tells Scott he needs Isaac, while Scott says he doesn't trust him. Playing along, Isaac speaks about himself in the third person, as if he isn't there, which is the way Scott and Derek are speaking about him. It's also a fun way to introduce a relationship that will undergo a lot of change and eventually evolve into something like a brotherhood.
"For Half Of My Childhood, I Was Locked In A Freezer So Being Helpful Is Kind Of A New Thing To Me."
Like a typical teenager, Stiles likes to make fun of Isaac for pretty much everything, especially his scarf, his sarcasm, and his useless comments. Even when Isaac becomes a part of Scott's pack as well as his friend group, Stiles singles Isaac out repeatedly. However, much to Stiles' frustration, Isaac always has an effective response prepared.
When Isaac refers to his awful childhood, Stiles only rolls his eyes and says, "Are we still milking that?" Even though Isaac is now living with Scott and Melissa, he uses any excuse he can to bring his past up. "Yeah, we are still milking that," he replies. Stiles may not mean these comments cruelly, but Isaac is right to speak about his struggles in an honest and vulnerable way, even if he does hide behind sarcasm. His friends should be more compassionate to him and understand he's doing his best.
"I Just Didn't Feel Like Doing Any Homework."
Fans often wonder when any of the teens in the show have time for schoolwork. Most days after school (and even during class time), they're off fighting the latest threat to Beacon Hills. When Isaac starts tagging along on the pack's adventures, Scott and his friends have to wonder he's so invested, because he clearly has no emotional interest in their battles.
When asked, Isaac says that he just didn't feel like doing homework. This is probably what most of the teens are thinking, but they are also passionate about defending their town. Isaac being Isaac, he brushes his feelings aside and tries to act nonchalant as usual.
"I'll Ask Later, It's Fine. Or Never. Yeah, I'm Good With Never."
Derek and Isaac have an interesting relationship as an Alpha and a Beta. Isaac is scared of Derek, but he won't admit it (much like Stiles). When the two of them are alone in the car, Isaac tries to make conversation, but he chooses the worst topic. Cora is sick and needs their help, but Isaac decides to not-so-subtly ask Derek if she's available.
Derek doesn't dignify his question with an answer, only death stares his Beta. Isaac then modifies his sentence and tries to act cool, but he actually feels threatened by Derek. From the first time Derek is introduced on the show, he's portrayed as a dark, mysterious figure whose thoughts can never be guessed by other characters. Isaac is no exception, and he never brings up Cora again.
"Dude, I Love Mexican."
In season 3, Scott is planning to meet Deucalion in secret, in an attempt to form a truce between their two packs. However, Isaac catches him on his way out and asks him where he's going. The conversation begins as a casual one, though viewers know that Scott is trying to deter Isaac. He's also still a little tense about Isaac dating Allison because he thinks that they're still going to end up together.
Scott tells him that he's going to get food, and when Isaac asks what kind, he says, "Mexican." This seems to convince Isaac, but Scott almost growls at him that he can eat alone. Isaac finds this response a little intense, but he accompanies him anyway - not to dinner, but the abandoned mall where Scott plans to meet Deucalion.
"She's The One With The Brown Hair. She's Kind Of Hot."
One of the main villains of season 3a is the darach, who turns out to be a new teacher at Beacon Hills. Nobody suspects Jennifer Blake for a long time. She doesn't seem like someone who could be an antagonist, and she's also perceived as conventionally attractive by characters like Isaac.
When Chris admits that he doesn't know which teacher is their target, Isaac gives him what he believes are the two most important markers of her appearance: "She's the one with the brown hair. She's kind of hot." This earns him a few odd looks from his friends, as well as some laughs from the audience.
"I Might Have Been On Watch Last."
Over time, Scott and Isaac become very close and trusting with each other. Melissa starts treating Isaac almost like a son, which includes her disciplinary methods. However, sometimes the boys let their egos get the better of them. For instance, Scott believes that he and Isaac should protect Melissa from potential evils by staying up at night to watch over her.
When Melissa wakes up one morning to find the boys passed out on the floor of her bedroom, they realize they failed. Neither is willing to admit that they dozed off on their watch, but Isaac finally crumbles under Scott's suspicious gaze. The scene is a humorous one, but it also shows that nobody can be expected to be able to save the world at every minute of the day.