I would nominate “Frankly my dear, I don’t give a damn.” from you-know-where, but since it was lifted from the book, (except for"frankly") I’m going to go with a different choice.
Therefore, I nominate this famous scene from the first National Lampoon’s Vacation.
Chevy Chase’s finest cinematic moment. A performance that surely brings back vacation memories for most of us.
Any other nominees?
“The Big Lebowski” is a masterpiece of profanity. The main characters swear frequently, intensely, and generally needlessly. The swearing is so naturally delivered it barely calls attention to itself, and it’s all in service of a great joke towards the end when Sam Elliot asks The Dude if he has to use so many cusswords. Similar to, in my mind, The Dude’s habitual White Russian consumption paying off in a spit take in the third act.
Steve Martin tries to rent a f***ing car in Planes, Trains & Automobiles.
I often find myself quoting Clive Owen in Shoot 'Em Up: “Fuck you, ya fucking fuckers!”
Kevin Kline in A Fish Called Wanda: “You’re the vulgarian, you FUCK!”
Peggy Wood in The Sound of Music: “What is you c*nt face?”
#1 on my list is Alec Baldwin in Glengarry Glen Ross. Just enough swearing thrown into a dynamite performance.
“Whats your name?”
“Fuck you! Thats my name.”
I know this doesn’t qualify because it wasn’t a movie, but I remember vividly as a teenager being totally hooked on ‘The Big Valley’, a Barbara Stanwyck cowboy/Bonanza type series.
I can still remember how my jaw dropped when one evening watching this totally tame 60’s western, Lee Majors’ character turned to another and said, “I’m your father’s bastard son!” :eek: I was like, what? they said ‘bastard’! on TV!!
Yeah, that just wasn’t done back then! As far as swearing goes, it wouldn’t raise an eyebrow now. But way back then? Yeah - it was way cool! 
The first one that comes to mind for me is Roy Scheider’s “Smile you son of a bitch” the moment before the shark meets its demise in “Jaws.”
Bruce Willis’ “Yippie-ki-yay, motherfucker,” from “Die Hard” is another memorable one.
Sometimes you just gotta say “What the fuck.” (Risky Business)
Yippee-ki-yay, motherfucker. (John McClane - Die Hard)
Oh, yeah - I remember that one quite well.
Midnight Run is full of gems. It’s been a while since I watched it.
“Now here come two words for you: Shut the fuck up”
“You slimeball swimming in a sea of pus!”
“I’m gonna fucking bust your head and I’ll put you back in that fucking hole and I’m gonna stick your head in the fucking toilet bowl and I’m gonna make it stay there.”
“You and that other dummy better start getting more personally involved in your work, or I’m gonna stab you through the heart with a fuckin’ pencil.”
The Blues Brothers visiting the Penguin.
While Glengarry Glen Ross is a masterpiece, the funniest and most effective use was in Slapshot, most notably this scene.
Kudos for including a German translation!
Raising Arizona: “Gimme that baby you warthog from hell!”
at about 1:50 here http://www.youtube.com/watch?v=2AIfVoGUs6c&playnext=1&list=PLBA8A5B7B2D70EFC6
“i am the motherfucking shore patrol motherfucker!” the last detail is jack nicholson at his out of control best, as mark twain would say, he knows the words and he knows the tune…
Kick Ass: “Ok you cunts. Let’s see what you can do now.”
You ah one ugly muddafucka.
-Predator
