Valerie: Bye-bye boys! Miracle Max: Have fun stormin' the castle! Valerie: (to Max) ...Think it'll work? Miracle Max: (to Valerie) It would take a miracle. Both: Buh-bye!
Apparently, Rob Reiner, who directed the movie, had to leave the set during the Miracle Max scene because he couldn't stop laughing and kept ruining the takes. He also laughed so hard it made him nauseous.
A fun fact: the only injury Mandy Patinkin sustained during filming was a bruised rib. He got it holding in his laughter while filming with Billy Crystal.
Cary Elwes is definitely Corpsing in a couple of shots.
"Get back, witch!" "I'm not a witch, I'm your wife! But after what you just said, I'm not even sure I want to be that anymore."
Vizzini's death scene: He laughs maniacally, then suddenly freezes mid-laugh, a grin permanently frozen on his face, and falls over, dead.
Not only does he fall over dead, he falls uphill.
Prior to it, we got this brilliant gem:
Man in Black: Truly you have a dizzying intellect. Vizzini: Wait 'til I get going! Where was I? Man in Black: Australia. Vizzini: Yes, Australia. And you must have suspected I would have known the powder's origin, so I can clearly not choose the wine in front of me. Man in Black: You're just stalling now. Vizzini:You'd like to think that, wouldn't you?! (continues stalling)
Man in Black:(smirks) You're trying to trick me into giving away something. It' won't work. Vizzini: It has worked! You've given everything away! And I know where the poison is! Man in Black:(calmly as ever) Then make your choice. Vizzini: I will! ...And I choose (gasps)what in the world could that be? (he switches the cups while the Man in Black turns around to look)
When the Albino wakes up Westley, first by speaking in a stereotypically raspy voice for an Igor, and then clearing his throat and speaking with a slight cockney accent.
The justly-named "Impressive Clergyman" from the infamous wedding scene arguably stole all the attention during the heroes' storming of the villain's castle. "Mawage. Mawage is wot bwings us togevvah tooday. Mawage, that bwessed awangment, that dweam wifin a dweam..." Note that while the Impressive Clergyman's speech impediment is Played for Laughs, Andre the Giant's actual speech impediment is not.
Near the end of the movie, Westley instructs Buttercup to tie Humperdinck to a chair. There's a cut to Inigo racing down the hall, while offscreen Westley says "Make it as tight as you like"... followed by an agonized grunt from Humperdinck.
Vizzini: No more rhymes now, I mean it! Fezzik: Anybody want a peanut? Vizzini:Dyeeeeargh!
Inigo: Give us the gate key. Yellin: I have no gate key. Inigo: Fezzik, tear his arms off. Yellin: Oh, you mean this gate key. [hands it to them]
Buttercup throwing herself down the hill.
Buttercup: You could die too, for all I care. (pushes "Man in Black" down a hill) Westley: (tumbling down a very steep ravine) AAAASSS YOOOUUU WIIISSSHHH Buttercup: ...Oh, my sweet Westley... What have I done? (Buttercup proceeds to throw herself down the hill)
Inigo's first encounter with Count Rugen.
Inigo: Hello. My name is Inigo Montoya. You killed my father. Prepare to die. Rugen: (gets into battle stance) (beat) Rugen: (runs for his life)
Continued in his and Inigo's fight to the death:
Inigo: HELLO! My name is Inigo Montoya. You killed my father! Prepare to die! Rugen:STOP SAYING THAT!!!
"HURRY UP! MOVE... THE THING! AND THAT OTHER THING!"
Inigo's horrible accent. The accent makes Mandy Patinkin's lines even funnier than if he said them without it.
"Let me 'splain ... No, there is too much. Let me sum up."
Westley: ...I mean, if we only had a wheelbarrow, that would be something. Inigo: Where we did we put that wheelbarrow the albino had? Fezzik: Over the albino, I think. Westley: Well, why didn't you list that among our assets in the first place? ...Oh, what I wouldn't give for a holocaust cloak. Inigo: There, we cannot help you. Fezzik:[produces a holocaust cloak] Will this do?
The battle between Fezzik and the Man in Black is one prolonged crowning moment of funny, starting with Vizzini giving Fezzik his instructions:
Vizzini: Finish him! Your way! Fezzik: Oh, good, my way. Thank you, Vizzini... what's my way? Vizzini: Pick up one of those rocks, get behind a boulder. In a few minutes the man in black will come running around the bend. The minute his head is in view, HIT IT WITH THE ROCK! [beat] Fezzik: ...My way's not very sportsmanlike.
Made even funnier on a meta level when you remember that at the time, Andre the Giant was still actively wrestling as a heel.
When Fezzik suggests he and the Man in Black fight fairly with no weapons:
Man in Black: You mean, you'll put down your rock and I'll put down my sword, and we'll try and kill each other like civilized people? Fezzik:(brings up giant rock) I could kill you now. Man in Black: Frankly, I think the odds are slightly in your favor at hand fighting. Fezzik: It's not my fault being the biggest and the strongest. I don't even exercise.
Man In Black: Look, are you just fiddling around with me or what? Fezzik: I just want you to feel you're doing well! I hate for people to die embarrassed!
Then when Fezzik is finally knocked unconscious:
Man In Black: I do not envy the headache that you will have when you awake, but till then, sleep well... and dream of large women.
Prince Humperdinck gets a few of his own:
She is alive, or was an hour ago. If she is otherwise when I find her... I shall be very put out.
Then this exchange with Rugen, which is also oddly heartwarming.
Rugen: Ah. Are you coming down into the pit? Wesley's got his strength back. I'm starting him on the machine tonight. Humperdinck: Tyrone, you know how much I love watching you work, but I've got my country's 500th anniversary to plan, my wedding to arrange, my wife to murder and Guilder to frame for it; I'm swamped. Rugen: Get some rest. If you haven't got your health, then you haven't got anything.
When Buttercup tries to escape her captors by jumping overboard:
Vizzini: Jump in after her! Inigo: I don't swim. Fezzik: I only dog paddle. (motions) Vizzini: AGGHH!
When Inigo has Rugen on the run, the Count eludes the Spainiard briefly by running into a room and locking the door behind him. Inigo, in a full panic that Rugen might get away, starts running and ramming himself against the door, trying to break it down, and screaming for Fezzik to help him out. Fezzik calmly walks up, stops Inigo from hitting the door, and punches it off its hinges with one fist. Then calmly turns and walks away as Inigo resumes the chase.
The entirety of Westley's "To the Pain" speech to Humperdinck, for how over-the-top his description is, commenting that Humperdinck would be "wallowing in freakish misery forever", and the various insults he throws at him, including such gems as "you miserable vomitous mass" and "you warthog-faced buffoon".
The look on Humperdinck's face after the last one (actually the first Westley said to him), followed by him visibly struggling for control as he says "That may be the first time in my life a man has dared insult me."
The book has a hilarious scene that didn't make it into the movie. After passing through a gauntlet of deadly animals to get to the Pit of Despair, Inigo and Fezzik reach an empty hallway going straight to a door. The narration explains that the emptiness is designed to lull intruders into a false sense of security so they'll immediately go for the door and awaken the venomous spider inside, which will bite and kill them. Great detail is devoted to how deadly this spider is. However, Fezzik is so frightened by nothing that he bolts and smashes through the door, "not even bothering with the niceties of the knob." Inigo goes to follow him, but notices a tiny spider skittering out from the wreckage of the door, which he promptly crushes with his boot.