This is one of my favorite Comedies and every line is amazing, but there's one subtle bit that kills me every time.
It's the scene where Sugar meets Junior on the beach, and Junior talks about spending time on his yacht. Here's the line:
Sugar: You own a yacht? (Turns around and points to one of the three yachts that are the same size.) Which one is it, the big one?
I laugh my ass off every time. Marilyn's delivery is perfect.

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Boy, with a screenplay this great how do you choose?
I'll put this one out there: Cary Grant Voice: "They shrink when they're marinated."
That line kills me!
Whistling Wolf should get more camera time . . . hes like a young Pacino!

I have quite a few favorites.
Joe - Anything today?
Nellie - Oh, it's you! Well you've got a lot of nerve!
Joe - Thank you! (Slams the door)
Joe - I'm Josephine.
Jerry - And I'm DAPHNE!
Joe - Hmm?
Sweet Sue - Goose it up a little!
Jerry - We'll try
Jerry - And bring your YACHT!
Osgood - But it's such a waste. A full moon, an empty yacht.
Jerry - I'll throw UP!
Sugar - I don't want you to think I'm a drinker. I can stop any time I want to, only I don't want to.
Jerry - It's like Jell-O on springs!
Osgood - Do you use a bow or do you pluck it?
Jerry - Most of the time I sssslap it!
Osgood - You must be quite a girl.
Jerry - Wanna bet?
Joe - Give him the teeth, the whole personality.
Osgood - Daphne?
Jerry - Hmm?
Osgood - You're leading again.
Jerry - Sorry.

"Pull the emergency brake!" Says Joe in response to Jerry asking what he should do if he really has to "go" but he didn't mean "use the toilet". They were on the train just bunking down. I swear, until today, when this film was shown on THIS TV I never really paid attention to that line. It's in reference to pleasuring oneself.
My other favorite lines were mentioned before about the surprise party and how Jerry could think of a million ways Sugar could thank him.
*The Manitou is in and will take your calls now.

"nobody's perfect"

"You tore off one of my chest"
I have been bent and broken, but, I hope, into a better shape, Grimm

You just tore the other one.
And the dead shall be raised incorruptible,and we shall be changed.~1 Corinthians 15:52

Hi blufftoni,
Yeah - that's a good one!
Best,
Ruben

just for the delivery:
i can never have children

So many wonderful lines:
The classic Osgood line 'Nobody's perfect.'
Daphne: I'm engaged, I'm engaged.
Geraldine: Guys don't marry guys. Why would you want to do that?
Daphne: Security!
There was also a line that Daphne said about smoking a cigarette but not inhaling - I recall President Clinton stating that about marijuana years after this movie was made.
Sugar: I always get the fuzzy end of the lollypop.
Osgood and Daphne dancing the tango with a rose in their mouth.
This is the best comedy classic with three wonderful stars and was so ahead of its time. They just don't make them like that anymore.
Best,
Ruben

Too many to count, but here are some contenders:

1. Jerry to "Junior": Bring your YACHT!!"
2. Jerry and Joe meet Sweet Sue:
   Joe: Hi, we're the new girls!
   Jerry: Brand new!
3. After he covers for her with Sweet Sue, Sugar asks Jerry if there's anything she can do for him to return the favor:
   Jerry: I can think of a million things.
   Sugar, hearing someone coming, jumps into his bunk with him.
   Jerry: That's one of them!
4. Jerry tells Osgood he can't fit into Osgood's mother's wedding dress, because he's not "built the same way."
   Osgood: We can have it altered.
   Jerry: Oh, no you don't!
   I'm not crying, you fool, I'm laughing!
   Hewwo.

"And where did you get that accent? NoboDy TalKs LiKe THaT!!"

In the frozen land of Nador they were forced to eat Robins minstrels. And there was much rejoicing.

That is sublime - I'm laughing just thinking about that scene. My favorite is in the train sleeper when Jack says "This may turn out to be a surprise party". Zowie!

That's a great line.
My favorite is the last line. Brown's reply when Jack Lemmon says "But I'm a man." Brown's reply: "Well, nobody's perfect."

The encounter between "Josephine" & the Bellboy when He is flirting with Her.
Josephine: Don't you think you are a little young for that Sonny?"
Bellboy: "Oh, you want to see my driver's license?"
the way Josephine reacts to his advances, and he so freely admits what he wants is priceless, love the way he delivers his lines.
"it's a Kafka high, you feel like a bug"

"Most of the time I ssssssslap it!"
"Well, make something up!"/RG

Sugar:
"They [the diamonds] must be worth their weight in gold!"
.
"What can be asserted without evidence can be dismissed without evidence."

Any line that came out of Osgood's mouth. XD "I like a girl with a shapely ankle" OMG hysterical!

"We wouldn't be caught dead with men"