[Leia sees someone listening to their conversation... Who turns around and hurriedly makes himself scarce.]
C-3PO: Excuse me sir, but mind if I speak to you? Han: What do you want? C-3PO: It's Princess Leia, she's been trying to get you on the comlink— Han: I turned it off, I don't wanna talk to her! C-3PO: Oh, well, Princess Leia is wondering about Master Luke. He hasn't come back yet. She doesn't know where he is. Han:I don't know where he is! C-3PO:Nobody knows where he is. Han: What do you mean nobody knows? C-3PO: Well, you see— Han: Deck officer? Deck officer!? C-3PO: Excuse me sir, but— [Han covers C-3PO's mouth, as he talks to the officer.] Han: Did anyone see Skywalker come in? Officer: No sir. It's possible he came in through the south entrance. Han: Possible? Why don't you go find out? It's getting dark outside. Officer: Yes sir. [Han removes his hand from 3PO] C-3PO: Excuse me sir, but mind if I ask what's going on? Han:(in deep thought) Why not? (walks away) C-3PO: Hmph. Impossible man. Come along R2. Just between ourselves, I think Master Luke is in considerable danger.
C-3PO must find Han's attitude aggravating:
C-3PO: Sir, if I may venture an opinion? Han: I'm not interested in your opinion, 3PO.
Yoda rummaging through Luke's supplies and beating on R2 with his stick when the droid interferes.
(Yoda gets Luke's little flashlight) Luke: Hey, give me that! Yoda: Mine! Or I will help you not! Luke: I don't want your help, I want my lamp back. I'm gonna need it to get out of this slimy mudhole. Yoda: Mudhole? Slimy? My home this is!
It gets even funnier after Luke orders R2 to back down. R2's arm withdraws into a panel, which Yoda proceeds to cheerfully tap shut with his stick.
Made even better by the prequels: R2 knows exactly who Yoda is and what he's pulling.
After Lando ratted out on Han and tried to gain Leia's trust by opening Chewie's handcuffs, Chewie decides to play Strango Calrissian
Additionally, as Lando is removing Chewie's handcuffs, Leia's saying, "Do you think that after what you did to Han, that we're going to trust—" And right as she finishes with "—you?", Chewie's hands are free, and he decides to, ahem, voice that opinion also. A bit more strenuously.
In an otherwise dark, foreboding scene, we have Leia's amused comment after Han punches Lando:
Leia: You certainly have a way with people.
"Laugh it up, fuzzball!"
"Why you stuck-up...half-witted...scruffy-looking...NERF HERDER!"
After Lando takes command of the Falcon, the look on Chewie and Leia's faces when the hyperdrive doesn't work for the third time in the film is just priceless. They just look at each other with incredulous resignation. And then Lando and Chewie start going crazy while Leia slumps dejectedly into a chair.
Lando: They told me they fixed it! I trusted them! It's not my fault! (Chewie then pushes Lando out of his way to fix it, again.)
"Artoo, come back here at once; you haven't finished with me yet! You don't know how to fix the hyperdrive! Chewbacca can do it! I'm standing here in pieces and you're having delusions of grandeur!" Of course, seconds later, Artoo does fix the hyperdrive. (And he slides bodily into a maintenance pit for his trouble.)
Plus, remember what is at the bottom of that maintenance pit: Chewbacca.
When 3PO finds another droid like him in Cloud City, he ends up getting dissed.
The look on Captain Piett's face during this is hilarious, trying to keep track of his conversation with Vader, while ignoring the man being slowly force-choked to death next to him. His surprised eye-twitch and his nod offscreen at the end are equally amusing, since he's basically giving the signal, "What he said. And, uh, can you please send someone to remove this body?"
When Captain Needa hops into a transport and flies to the Executor to inform Vader that the Millenium Falcon has escaped, the next shot is of him doubled-over as he dies, while Vader steps around his corpse.
Darth Vader: "Apology accepted, Captain Needa."
Luke's reaction to Leia's kiss, and Han's reaction to both.
Also C-3PO's reaction to the entire situation.
Possibly Han's best line ever:
C-3PO: Sir, it's quite possible this asteroid is not entirely stable.
C-3PO: Sometimes I just don't understand human behaviors. After all, I'm only doing my job...
While briefing the Bounty Hunters on he pursuit of the Millennium Falcon, He tells them that he wants the crew alive, then specifically turns to Boba Fett and calls him out:
Boba Fett: As you wish.
It's a quick moment, but after the Falcon finally gets away from Vader and company at the end, Vader turns away from the window, then does a brief double-take back to the window as if to say, "What? Seriously?"