Any single time Olive uses Facial Dialogue to express her snark. One notable example, taken from "Oscar the Couch", has her sporting this expression after Oscar tells her the difference between the Snow-Go-Away-inator and the Make-Snow-Disappear-inator (one has a handle, the other doesn't).
"Zero Effect" has Ms. O introducing Glenn, a cupcake shop owner, to the partner pair, and as he begins talking about the various flavors he's going to have (one million-billion-trillion, as a matter of fact), Otto's expression turns from mild intrigue to absolute delight while all Olive can do is stare at her partner in shock.
Otto gives a Big "NO!" as Olive tells Polly Graph about how zeroes are disappearing around town, and then he cuts himself off to ask why it's a big deal. What's even funnier is that he is well aware of the issue since Ms. O had gotten him and his partner up to speed a minute earlier.
And directly after that, he winds up with an armful of Polly Graph's mini marshmallows as Olive is giving the mathematical Aesop, which he begins eating. Once she's done, Polly tells him:
Polly: You know you gotta pay for that, right?
[Otto looks at her with his mouth full of marshmallows]
When telling Otto to Get A Hold Of Yourself Man, Olive goes off on a dramatic tangent on how they'll find the number hog if they have to climb the highest mountains or swim the deepest oceans...before she's interrupted by Oscar holding his Number Hog Finder gadget. She hands Otto his invitation back, grabs the gadget, and says, "That'll work."
Olive's meltdown when destroying Glenn's banner. It's quite amusing to see Otto be the Only Sane Man and act like a father that's trying to control his tantrum-throwing child, while Glenn reacts in pure shock.
When imitating the Burly Bears' Grizzly Bear Growl move, Olive aims it at Ms. O of all people, who leans back and fixes her with a confused expression.
Olive's general fangirling in the episode most definitely counts.
"Soundcheck" has a fair number of hilarious moments, but by far the best part has to be Olive's complete disdain for the band. This only gets heightened with how everyone in the town seems to be completely overjoyed by the new song, except for her. The episode is essentially 11 minutes of Olive being absolutely tortured by the song. Even Ms. O loves the band!
When Otto, the town baker, and a man whose tires were removed from his car begin singing the chorus of the band's newest song, Olive simply looks up and asks in sheer despair, "Why is this my life?"
Towards the end...
Olive: You know how I always said Soundcheck was...nyeeeee?
Olive: (Beat, before talking in a sassy voice) I feel the exact same way.
Not to mention after already rewriting the song to fix the problem of it making things disappear, when they find out it's now adding four of everything...
Ms. O: REMIIIX!
Olive: NOOOOOOOOOOOOOOO![Cue her getting on her arms and knees and crawling away in horror while Ms. O and Otto dance in the most over-the-top way]
"Oscar of All Trades" has the montage of Oscar's failed career-tracks before he became a scientist, which happened because he was the go-to guy for fixing (and creating) everyone's gadgets, which many other agents had... problems with. This is illustrated by Olaf, who'd been working on a Potato-inator for three years.
Olaf: (despondently, while haphazardly assembling a gadget) This is not my skill-set.
It also reveals that Doctor O's prior job within Odd Squad was gift-shop cashier.
Otis' heartwarming encouragement to Olympia turn funny when he points out that she didn't realize he was being talkative (for Otis) because he talks less than than most people and Olympia talks way more, and again when he ends his speech with a quietly-desperate, "Can we please stop talking about feelings now?"
Orchid's mind-game during her interview with Oscar and Doctor O.
Throughout the episode the villains try to collaborate. At the end, they give up and decide to do whatever they want. The Shapeshifter notes that it seems like they failed to work together, but decides to look at it as them learning a valuable lesson in thinking for themselves.
"The Saddest Song in the World of All Time." It's every bit as ridiculous as it sounds. Ms. O's Skyward Scream of agony after being told to get her own juice box by another girl has to be the best part. However, it also doubles as a Tear Jerker, since the song is paired with the montage of Ms. O, Otis, Olympia and Oona and their lives after Odd Squad disbands.