A lot of moments where Tutter the mouse gets caught up in the moment, but then utters out "Oh... thank you Beaaaar!". What sells it is the way he says it.
In one episode, the cast is having a picnic and Bear is trying to convince Treelo that they should have fruits and vegetables other than just bananas (or "bananananas," as Treelo calls them.) He eventually convinces Treelo that they should bring tomatoes, but when he tells Treelo to put the tomato in the picnic basket, Treelo clutches the tomato and says that it's his friend. "The tomato is your friend?" deadpans Bear, casting an Aside Glance at the audience.
This later causes Tutter to cry out incredulously "IT'S A TOMATO!!!!!"
When agitated, Tutter has a tendency to swear by shouting out names of cheeses, such as "Oh, Cheddar Chunks!", "Oh, Gouda!", "Oh, Brie!", or even "Great Gobs of Gorgonzola!".
Harry the Duck rigidly insists on referring to Bear as "Mr. Bear," even though Bear tells him repeatedly "...Oh, and Harry? It's just Bear."
In "A Beary Bear Christmas," the kids are bickering about holiday preparations. Bear sort of shouts out them a bit to try to get their attention, then sings a bit of the show theme to remind them that he's still there.
Also in "A Beary Bear Christmas," Bear invites Jack to stay in the Big Blue House for a while and rest. Jack had been protesting up to that point that he needed to move along, but at this he flops over on the couch and immediately dozes off. Tutter stares in disbelief and makes a comment to either nobody in particular, or to the audience.
Tutter: (incredulous) He's sleepin'!
So much of the "Potty Time with Bear" episode, particularly the "Toileteers."
"Santa Hogg" having to listen to the kids' increasingly outrageous Christmas wishes in "A Beary Bear Christmas" and his expression.
Tutter: Just... tons and tons of cheese! Limburgers and Bries...
"Raiders of the Lost Cheese" - Tutter leads his friends on a quest to find the "great lost cheese," his great grandpa Tutterly T. Tutter's legendary treasure. They find it, alright, and, of course, it turns out to be all old, moldy and nasty. Heh. What did they expect?
From the "Imagine That" song from the episode by the same name...
Ojo: I could be Bear!
Bear: You could?
Ojo: Do you always smell this good? Hey, Bear! That sounds just like you.
Ojo's song all about her from "You Go, Ojo!" is performed by her and Bear. Despite this, she still manages to insert herself in the boys' song, "Oh, Boy" from "Boys Will Be Boys."
Pip and Pop: Let's go chase the squirrels.
Bear: Oh, boy
Ojo: Let's play with the girls!
Just the fact that the show did certain songs in certain styles. For example, "Otter Love" is performed as an R&B / soul ballad with rap inserts from Bear. "It's so rare / The way you care / Go on, declare / Share your love." Another song, "Find the Words," is performed by Bear as a gospel spiritual. "You got to say / The words, hallelujah / Come on and say the words!"
From the "Dear Grandma" song, performed by Tutter - "Thanks for the chocolate cakes covered in cheese / For teaching me how to say 'thanks' in Chinese!"note It's "xie xie" for those who might be wondering, though that's never actually mentioned in the song itself. Yeah, Tutter just thanked his Grandma Flutter for teaching him how to say "thanks."