In "Disturbing Behavior, he and Sheriff Forbes are discussing Bill, her gay ex-husband and Caroline's father. Damon suggests killing him.
Sheriff: Just because we're on good terms doesn't mean I'm okay with your...lifestyle
Damon: Is that what you told him when you got divorced?
Almost every scene with Stefan at the beginning of the party in "Under Control" Specifically because it's very clear that he's not okay, and suffering terribly from the urge to drink human blood. What brings this into the funny territory is his arguing back and forth with Damon all while all this while twitching and jerking around like someone going through very real withdrawawl. Of course this is before things start to become serious...
After Tyler notices several clues about Caroline, he finally confronts her with his suspicion that...she's a werewolf.
In "The Descent" Caroline is kissing with Matt and shortly after that - with Tyler. She doesn't take it well:
Caroline: "Everyone just needs to stop kissing me!"
In "Daddy Issues" John keeps repeating to Elena that he wants to protect her. Her angry answer?
Elena: Got it. Get in line.
The look on Stefan and Damon's faces when they realize that they have accidentally created a secret superweapon.
Klaus talking about the '60s, which "pretty much sucked" except for the Beatles.
Damon's impersonation of vampires and Elena when giving a summary of what happened at the 50's dance.
Damon: "And the vampires were all 'GRRR!' and you were all 'AAAH'!"
Alaric needs to prove his identity, and brings up Jeremy walking in on him and Jenna while they were having sex causing Jenna to quickly say, "Okay, it's him!"
Elijah running out of the Salvatore house after realizing he needed to be invited in
Anytime Damon and Bonnie have a conversation. Especially in one episode when Bonnie sees that Damon has the wooden stake that will kill Klaus.
In "The Hybrid" after Alaric finishes explaining his nature know-how
Elena: "You were a boy scout, weren't you?"
Alaric: (mutters) "Shut up"
Later Elena pours some vervain water on some ropes.
Elena: "Ric, take these" (Damon reaches for the ropes and is burned) "I said Ric"
Damon's half hearted attempts at apologies to Mason Lockwood and Alaric in "Ghost World"
As Damon hides his original-killing stake under the house's firewood:
Alaric: Did you learn nothing from the moonstone in the soap dish?
Damon: Why, where'd you hide yours?
Klaus and Rebekah bicker like the siblings they are, over the best way to torture Damon.
Klaus reading Caroline's Miss Mystic Falls application in "My Brother's Keeper".
Prof. Shane fanboying over Rebekah & Kol much like a good amount of the fandom would.
Shane: Rebekah and Kol Mikaelson, two Originals! I can't believe it! This is such a trip!
Shane again when he and the others land on the island where Silas is sealed. The first he does is offer Damon sunscreen. Think about it.
Kol, when he's about to cut off Jeremy's Hunter arm to stop them from raising Silas. First he reassures Jeremy, and just as he's going to do it, he asks out loud "Which one is it?" with this childish confusion on his face. And then he just shrugs and decides to cut off both arms, just to be sure.
Rebekah gets one in 'Into the Wild,' when she lists out the reasons why Elena's presence is unnecessary on the island: "Shane is the walking compass, Jeremy has the Hunter's mark, Bonnie's the witch to break the spell, and Stefan and I are keeping an eye on the tombstone."
Caroline's Oh Crap expression when, in 4x18, both she and Klaus understand just how much of her actual feelings for him she has revealed by angrily stating she should have turned her back on him ages ago (and realize she hasn't), as well as how close to each other they're standing. Crosses as a Crowning Moment of Heartwarming, albeit a strange one, and a They Really Do Love Each Other one.
The sheer irony, near the end of 4x18, that, whilst Katherine is for once acting like Elena would, demonstrating her love for Elijah by entrusting him with the Cure and thus giving him decisional power over her life and their relationship, Elena instead acts like Katherine always did, with coldness and cruelty, by threathening to kill people until Stefan and Damon give up on trying to give her the Cure and by killing an Innocent Bystander to drive the point home.
In the same episode, Rebekah, Damon, and Stefan's collective reaction to finding out that Katherine is sleeping with Elijah. Especially funny how each of them makes a slightly different variation on the classic "EW".
Rebekah coaching Elena on how to act like Katherine. The two of them seem to be having a lot of fun with it.
When Rebekah snaps Caroline out of the trance Silas put her in by slapping her, Care's response is, "Bitch!"
Alaric proving he's not Silas by revealing their secret liquor stash in a locker.
In the season five premire, Jeremy walking in on Damon and Elena.