What are some classic scenes from movies that never fail to make you laugh?

Most of the scenes in Dogma.

Hen-pecked husband Harold Bissonette (W.C. Fields) trying to sleep on a porch swing in “It’s a Gift.” The series of bits in this scene, some of them from Field’s vaudeville routines, is laugh-out-loud funny to me every time I see it

The stateroom scene from Night at the Opera.

When they about to do ‘sex’,it’s completely censored but sometime you can hear the scream and moan before they censored the whole ‘sex scene’. Ha ha ha (naughty smile).

The chain-reaction scenes in The Money Pit.

Several moments in O Brother, Where Art Thou?—my favorite being when George Clooney says that he’s the only one who remains unaffiliated. He looks like he’s about to crack up.

And, unfailingly, the restaurant scene in Being John Malkovitch.

Zero Mostel screaming “I want that money!!!!” in the Producers.

The big speech on dicks, assholes, and pussys in Team America World Police.

Woody Allen fighting the giant boob in Everything You Ever Wanted To Know About Sex.

Pretty much the entire movie of Young Frankenstein and Monty Python’s Holy Grail.

The entire squirrel bit with Kathy Bates in Rat Race.

Fast Times at Ridgemont High – Jeff Spickoli talking about Jefferson’s wrecked car
“Trust me dude, I can fix it. My dad’s got all kinds of gnarly tools, he’s a plumber.”
The whole movie pretty much still cracks me up.

A couple of scenes from Good Morning Vietnam: The faked radio interview with Richard Nixon when he questions Nixon about his genitals and sex life and the scene between Cronauer and the general and the general and Sgr Major Dickerson about his transfer including the repeat of the line “More dire need of a blowjob than any white man in history” and many other scenes from this movie.

“And to think all this time, it was your cup that was poisoned.”
“They were both poison. I spent the last few years building up an immunity to iocane powder.”

A couple of the many scenes in The Full Monte:
When they are all standing in the unemployment line after a rehearsal was busted by the cops and gradually they all start dancing in unison when their song comes on,
When the cops review their strop video and one of them says “he is leading”
When Gaz and company are reviewing new dancers and Horse shows his stuff and Gaz says “Gentlemen the lunchbox has landed”
When they ruin Gerald’s interview by parading Gerald’s garden gnomes outside the window so he can see them
and many more

Tom Jones 1963
Most of the dialogues between Squire Western and Miss Western [typ—brother, you are a boor! A boar? I am not a boar!

The last scene in “Some Like it Hot.” And Joe E. Brown’s last sentence for “Perfect Last Sentence in a Movie.”

& the fantastically great answer goes to @YARNLADY for her Princess Bride quote!!

My favorite scene from that movie is:

Westley approaches the boulders & slows down.

A hurled rock shatters into dust against the face of the boulder just in front of him. He turns to see Fezzik, picking up another rock.

Fezzik: I did that on purpose. I didn’t have to miss.

Westley: I believe you.

That scene, with that dialog… makes me laugh every time.

”those aren’t PILLOWS!”
————————————————————
“Does your dog bite?”
“No.”
GROWL, MUNCH, CHOMP
“I thought you said your dog does not bite!”
“That’s not my dog.”

Oh g-d @cprevite, I love both of those, but particularly the Pink Panther one!

It this one movie and I cannot for the life of me remember the name or who played in it. But in this one scene this guy was pushed down the stairs, and as he was falling he said ‘A! E! I! O! UUUU!’ – aeiou (while bumping down each step). I know I’m hardly explaining it right, but it was the most hilarious scene.

Like @Jeruba most of O Brother, Where Art Thou cracks me up, and I’ve seen it too many times to count. When they are in the car with Baby Face Nelson and his money is blowing around and Delmar tells him “Friend? You’re folding money’s come unstove” it gets me every time for some reason.

Also in Forrest Gump when he shows his butt to the president, LBJ? it is hilarious.

In Monty Python’s The Meaning of Life when they sing the Every Sperm is Sacred song, I just love it. And right before the song when the mother of all the children is washing dishes and a baby falls out she says to one of the older children “Get that for me would you, Diedre?” like it was nothing. Oh how I love Python.

Blazing Saddles (1974), since Python stuff has been mentioned already. Shoot, the entire movie never fails to make me laugh:

Sheriff Bart: Are we awake?
The Waco Kid: We’re not sure… Are we… black?
Sheriff Bart: Yes, we are.
The Waco Kid: Then we’re awake, but were very puzzled.
____________________________________
The Governor: I didn’t get a ‘HARUMPF’ outta that guy!
Hedley Lamarr: Give the Governor a ’HARUMPF’!
____________________________________

Hedley Lamarr: I’ve decided to launch an attack that will reduce Rock Ridge to ashes.
Taggart: Well, whaddya want me to do?
Hedley Lamarr: I want you to round up every vicious criminal and gunslinger in the West. Take this down. I want rustlers, cut throats, murderers, bounty hunters, desperados, mugs, pugs, thugs, nitwits, halfwits, dimwits, vipers, snipers, con men, Indian agents, Mexican bandits, muggers, buggerers, bushwhackers, hornswagglers, train robbers, shit kickers and Methodists!

This from Singin’ in the Rain (1951) Lina is ready to shoot her first sound film scene in 18th century costume, including the high wig:

Lina Lamont: Gee, this wig weighs a ton! What dope’d wear a thing like this?
Rosco: Everybody used to wear them, Lina.
Lina Lamont: Well, then everybody was a dope!

Hancock – with the little French boy -“Say asshole one more time.”

Give Me The Bat Wendy or Wednesday night as we like to call it.

Random, but in Gone with the Wind, when Scarlett is running to her father at the beginning of the movie, in that big white puffy dress, on the side of that gross looking creek..
I always laugh. I always made a joke about how funny it would be, watching her running along the creek, giggling, just to fall and get the entire gown all muddy.

King Arthur: Old woman.
Dennis: Man.
King Arthur: Man, sorry. What knight lives in that castle over there?
Dennis: I’m 37.
King Arthur: What?
Dennis: I’m 37. I’m not old.
King Arthur: Well I can’t just call you “man”.
Dennis: Well you could say “Dennis”.
King Arthur: I didn’t know you were called Dennis.
Dennis: Well you didn’t bother to find out did you?
King Arthur: I did say sorry about the “old woman”, but from behind you looked…
Dennis: What I object to is you automatically treat me like an inferior.
King Arthur: Well I am king.
Dennis: Oh, king eh? Very nice. And how’d you get that, eh? By exploiting the workers. By hanging on to outdated imperialist dogma which perpetuates the economic and social differences in our society.
__________________________________________________________________

King Arthur: I am your king.
Woman: Well I didn’t vote for you.
King Arthur: You don’t vote for kings.
Woman: Well how’d you become king then?
[Angelic music plays… ]
King Arthur: The Lady of the Lake, her arm clad in the purest shimmering samite held aloft Excalibur from the bosom of the water, signifying by divine providence that I, Arthur, was to carry Excalibur. THAT is why I am your king.
Dennis: [interrupting] Listen, strange women lyin’ in ponds distributin’ swords is no basis for a system of government. Supreme executive power derives from a mandate from the masses, not from some farcical aquatic ceremony.
__________________________________________________________________________

Dennis: Oh, but you can’t expect to wield supreme executive power just because some watery tart threw a sword at you.
Dennis: Oh but if I went ‘round sayin’ I was Emperor, just because some moistened bint lobbed a scimitar at me, they’d put me away.
Dennis: Come and see the violence inherent in the system. Help! Help! I’m being repressed!
King Arthur: Bloody peasant!
Dennis: Oh, what a giveaway! Did you hear that? Did you hear that, eh? That’s what I’m on about! Did you see him repressing me? You saw him, Didn’t you?

Airplane!- Autopilot

The fart scene in Blazing Saddles

@anartist We always laugh about how much my Dad laughed at that scene!

In Planes, Trains and Automobiles John Candy’s loop on his coat sleeve gets wrapped around a seat button so he can’t steer with that hand. Then his Other sleeve gets caught on a seat button; now he cant steer with Either hand. Gets me laughing every time.
In Uncle Buck, John Candy brings out an ax from the trunk of his car and shows it to this girl’s boyfriend (he’s babysitting for the girl and she resents it so they continue kissing.) Waving the ax, he tells the boyfriend “I’ve been known to circumcise an ant with this; come closer and take a look.”

@Aster You’re forgetting the best scene of all in Uncle Buck… “Hmm, unbreakable glass.”

When I first watched that movie – when he smashed that plate – I had never laughed so hard in my life.

John Candy in Uncle Buck . . . “I’m Buck Melanoma. Moley Russell’s Wart.”

“Home Alone” with Maccaulay Culkin. The entire movie is so silly, so unreal, and such a big joke, it makes me laugh.

‘I just went GAY all of a sudden!’

From Bringing up Baby with Katherine Hepburn and Cary Grant.