Chuck and Blair's plot in episode 303 is really one Crowning Moment of Funny after another. From Blair's reaction to finding Dan in bed with Georgina ("I'm wearing a glove and I still want to wash my hands!") to their bidding war at the auction. And of course, "She stole my shoes?"
In season one when the NJBC tries to get Serena to open up about her horrible secret by pointing out that all of them have done bad things. Doubles as a Crowning Moment Of Awesome for Chuck.
Blair: I had sex with [Chuck] in the back of a limo.
Chuck: Several times.
Nate: And I had sex with [Serena] at a wedding, when I was [Blair's] date. (glares at Chuck) Once.
Chuck: I'm Chuck Bass.
Dan and Eric's first attempt to break the peace treaty between Chuck and Blair, which crashes and fails so spectacularly it qualifies as an Epic Fail. Dan walks into Chuck's house, awkwardly pretends to be there to see Nate, then stumbles through saying that Blair slept with Jack (again) and that he should get revenge by offering protection to Jenny. Blair casually walks out of the shadows and says "You're about six months too late, Humphrey." She and Chuck then sit down and casually patronize him while sipping whiskey.
And, later, everyone mentioning their guesses as to Blair's biggest secret. Eric: Something a little bit more American Psycho. Not stabbing a homeless man, but at least feeding a cat to an ATM. Penelope: A Jack Bass sex tape! Tiffany: Nelly Yuki snuff film? They're all wrong: it's Blair getting on stage drunkenly while at a concert with Chuck, to sing Stand By Your Man.
Serena's rebellion against Bart. "Oh, I forgot to put on underwear!"
Georgina Sparks running into Chuck at Oh My Jesus Christ camp.
Georgina: Chuck Bass! (excited hug) Have you been saved too?
Serena, with near idol worship, declaring: "I didn't know that you could cook" when Nate shoves a waffle in a toaster.
Dan singing to Milo:
Dan: (in song) This loft is your loft. This loft is my loft. Where's your Aunt Jenny? She moved to Hudson. She... wears leggings...
Blair and Chuck negotiating a peace treaty... for about five hours whilst Nate and Serena look on in astonishment.
After the last episode ended with crazy hate sex with Blair and Chuck on a piano. The next episode opened with...Blair in her bed. Alone. Serena came in for a brief conversation, during which Blair casually remarked that she hated it when the duvet puffed up. Serena leaves and the covers are thrown back to reveal...none other than CHUCK BASS.
The Dean turning to Vanessa and going, "Excuse me, who are you?"
This exchange when Chuck has been caught getting high on school property:
Headmistress Queller: I found Charles smoking marijuana on school property.
Chuck: It was hash actually. I find it gives a softer high.
Jack: (nodding) Right. (to Queller) The evidence seems questionable.
Jack in the second last episode of the fourth season. During a tense, emotional scene, he keeps wandering in and out with wonderful pithy comments:
Jack: Can we just call the cops? I'm hungry. And all you seem to have are olives and hallucinogenic mushrooms.
Blair: New minion!
New Minion: Emily!
Dorota: She has no time to care.
Blair taking down Georgina: "Haven't you heard? I'm the crazy bitch around here."