The Improbability drive turning them into yarn dools. Arthur throws up rainbow yarn, then cuts to human arthur pulling the last of it out of his mouth.
The entire "whale and petunia falling to the planet" sequence.
"I wonder if it'll be friends with me?"
"Curiously enough, the only thing that went through the mind of the bowl of petunias as it fell was, 'Oh, No... Not Again!'. Many people have speculated that if we knew exactly why the bowl of petunias had thought that we would know a lot more about the nature of the universe than we do now."
Arthur and Ford imprisoned in the Vogon ship.
Arthur: It's at times like this I wish I'd listened to what my mother told me. Ford: Why, what did she tell you? Arthur: I don't know, I didn't listen.
And of course the scene with Zaphod and the Total Perspective Vortex. "Hey, is that a piece of fairy cake?"
"If I told you how much I needed this," he said ravenously, "I wouldn't have time to eat it." He ate it.
Just the name 'Dr. Dan Streetmentioner'.
Oolon Coluphid's Trilogy of Philosophical Blockbusters: Where God Went Wrong, Some More of God's Greatest Mistakes and Who is this God person anyway?
Well, That About Wraps It Up for God.
"Before time, the Universe was created. This was very unpopular, and is often cited as a bad move."
"They found only an old man who claimed that nothing was true, although he was later discovered to be lying".
Ford: That's beside the point! The point is that I'm turning into a "perfectly safe" penguin, and my colleague here is rapidly running out of limbs! Arthur: Oh, that's all right, I've got them all back now...admittedly, they're a little longer than I'm used to.
Ford trying to retain his intellectuality and explain the universe while hammered!
Two in the Frogstar Scout Robot scene. First:
*scout robot whizzes past*
Zaphod: What was that?
Hitchiker: Frogstar scout robot class A looking for you.
*larger scout robot whizzes past*
Zaphod: And that was...
Hitchiker: Frogstar scout robot class B looking for you.
Zaphod: And that?
Hitchiker: Frogstar scout robot class C looking for you.
*gigantic tank-shaped robot rumbles into view and demolishes nearby building with its tracks*
Zaphod: Holy photon, what's that?
Hitchiker: A tank. Frogstar scout robot class D come to get you.
This bit becomes even funnier in the radio version, where it's revealed that the scout robots actually knew Zaphod was there, and called the Frogstar tank to get him.
Second: Marvin has been left alone with no weapons to deal with this tank-robot. After a long guessing game in which the tank tries to discover what they've armed Marvin with to stop him, he finds out they didn't give him anything.
Marvin: I'll tell you what they gave me to protect myself with shall I?
Tank: Yes, alright.
Marvin: Nothing at all, not an electronic sausage.
The tank, after ranting some more, decides to take out his anger:
Tank: I think I'll smash the wall down! *does so* I think I'll shoot down their bloody ceiling as well! *does so*
Marvin: That's very impressive.
Tank: You ain't seen nothing yet, I'll take out this floor too, no trouble! *does so... and falls down*
Tank: Hell's bells! *smashes itself to bits on the ground fifteen stories below*
"For a moment, nothing happened. Then, after a second or so, nothing continued to happen."
This little exchange:
Ford:How do you feel? Arthur: Like a military academy. Bits of Me Keep Passing Out. [pause] Arthur: If I asked you where the hell we were, would I regret it? Ford: We're safe. Arthur: Oh good. Ford: We're in a small galley cabin in one of the spaceships of the Vogon Constructor Fleet. Arthur: Ah. This is obviously some strange usage of the word "safe" I wasn't previously aware of.
"We're going to get lynched, aren't we?"
"Vell, Zaphod's just zis guy, you know?"
Specific to the TV series
The illustration that pops up when the Guide says, "Most leading theologians claim that this argument is a load of dingo's kidneys..."
During the entry on Vogon Constructor Fleets, the visuals during the last part.
First, "The best way to get a drink from a Vogon is to stick your finger down his throat..."—image is simply text to the effect of "It's too disgusting to show you".
Second. "...and the best way to irritate him is to feed his grandmother to the Ravenous Bugblatter Beast of Traal." First it shows the same images of the Vogon grandmother and the Beast from earlier in the entry, then it shows the latter actually eating the former.
Specific to the books
The Hitchhiker's Guide to the Galaxy
Oh sweet Jesus, everything. Just in the first few pages there's the bit about the word 'bulldozer' going through Arthur's head, Arthur in the mud, Genghis Khan, putting a bag over your head when the world is ending . . . trying to describe it all would barely be shorter than simply posting the entire thing.
The foreman in the first book, who is distantly descended from Genghis Khan and repeatedly has urges to go tearing around the countryside doing the standard maim pillage burn routine.
"...with two large axes crossed over the front door. His wife wanted hanging roses, but he wanted axes. He didn't know why, he just liked axes."
This bit of dialogue a fantastic commentary on the human condition, and is delivered absolutely perfectly in the television version.
"I'd rather be happy than right."
"And are you?"
"No. That's where it all falls down, of course."
The feelings that Deep Thought has for other computers. "The Milliard Gargantubrain?" said Deep Thought with unconcealed contempt. "A mere abacus - mention it not."
The Restaurant at the End of the Universe
"In the beginning the Universe was created. This had made a lot of people very angry and had been widely regarded as a bad move."
In the second book, The Heart of Gold was being attacked by a Vogon ship and they couldn't move because the ship computer was too busy trying to make tea. The force-shield started blistering and cracking under the sudden, unexpected attack. Ford thought it would probably hold for about four minutes...
"Three minutes and fifty seconds," he said a short while later.
"Forty-five seconds," he added at the appropriate time. He flicked idly at some useless switches, then gave Arthur an unfriendly look.
"Dying for a cup of tea, eh?" he said. "Three minutes and forty seconds."
"Will you stop counting!" snarled Zaphod.
"Yes," said Ford Prefect, "In three minutes and thirty-five seconds."
The original version of that exchange (in the radio program) was also hilarious:
Arthur: I'm sorry, it's just that I was dying for a cup of tea!
Zaphod: You soon will be, baby!
The Dangers Of Teleportation
I teleported home one night
With Ron and Sid and Meg
Ron stole Meggie's heart away
And I got Sidney's leg.
The first thing that hit their eyes was what appeared to be a coffin. [pause] And the next four thousand nine hundred ninety-nine things that hit their eyes were also coffins.
The Golgafrinchans are fairly stupid, but the Captain is absolutely hilarious.
Number Two: Sir! They are trespassing on the ship!
Captain: Oh, I expect that they probably just dropped in for a quick jynnan tonnyx, don't you, Number Two?
And then later...
Number Two: May I remind you... that you have been in that bath for three years?!
Life, the Universe and Everything
The whole "Eddies in the space-time continuum." confusion is hilarious.
Ford's elaboration on his temporary madness right before it is even better.
Arthur: I thought you must be dead... Ford: So did I for a while, and then I decided I was a lemon for a couple of weeks. I kept myself amused all that time jumping in and out of a gin and tonic. Arthur: Where did you...? Ford: Find a gin and tonic? I found a small lake that thought it was a gin and tonic, and jumped in and out of that. At least, I think it thought it was a gin and tonic. I may have been imagining it.
"There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss."
"...except for your sudden obsession with whelks."
The entire Agrajag sequence is quite possibly the funniest segment ever put to prose.
Not to mention the fact that it is the punch line of the funniest Brick Joke in literature.
Made even funnier in the audiobook, due to Agrajag being a Large Ham.
So Long, and Thanks for All the Fish
The old lady on the plane, looking on as Arthur and Fenchurch join the mile-high club in the most unconventional way possible.
Ford delibrately running up huge expenses as a restaurant critic, culminating in trying to charge the purchase of London Zoo and the entire hotel he is staying in to room service.
And Another Thing...
Whatever else you may have to say about And Another Thing..., most of the business with the cows desperate to be eaten were pretty funny, especially the "I'll track down your entire family and not eat them!" bit.
The airlock scene has an awesome moment of false hope being crushed for laughs: "So this is it? We're going to die?" "Yea, we're going to . . . No, no what's this? This . . . this is nothing; we're going to die."
"Ford?" "Yes?" "I think I'm a sofa." "I know how you feel."
In the other, Arthur is about to embark on his tour of the planet factory, when he beats up Slartibartfast, rescues a random dog and runs off, with Bill Nighy left Chewing the Scenery in his wake.
Ford and Arthur's reactions to Vogon poetry: Ford writhing in agony, Arthur... not so much.
Hearing Mos Def say the line "What if I told you I wasn't from Guildford?"
The answering machine message left at Magrathea...
Councilman: As a token of our appreciation, we hope will you enjoy the two thermonuclear missiles we just sent to converge with your craft. To ensure ongoing quality of service, your death may be monitored for training purposes. Thank you.
This exchange when Ford and Zaphod try to convince Arthur to enter a portal...
Arthur: We can't just jump into that-... that! We don't even know where it leads!
Ford: If we- If we pick the wrong, we just- we come back; we pick another one. It's no biggy!