The famous scene from Gourmet Night when Basil's car breaks down and he starts screaming hysterically at it before running off-screen... only to return to hit it with an uprooted tree repeatedly.
"Right! That's it! I'm going to give you a damn good thrashing!"
The funniest part is when Basil gets in the car and goes crazy, he doesn't turn the key.
The UK company Corgi is well-known for its die-cast models of movie and TV cars. When it put out a model of Basil's 1100, of course the car had an accompanying figurine of Basil about to give it a good thrashing.
Word of God is that it took forever to find just the right kind of tree branch for the scene, too.
Basil Fawlty: That is Torquay, ma'am. Mrs. Richards: That is not good enough. Basil Fawlty: Well, may I ask what you were expecting to see out of a Torquay hotel bedroom window? Sydney Opera House, perhaps? The Hanging Gardens of Babylon? Herds of wildebeest sweeping majestically... Mrs. Richards: Don't be silly, I expected to see the sea. Basil Fawlty: You can see the sea: it's over there between the land and the sky!
"No, the radio works. You don't."
"This is MINE!" (cue maniacal laughter)
Sybill: If I find out the money on that horse was yours you know what I'll do Basil.
Basil: You'll have to sew 'em back on first!
The charade scene: Polly guessing 'small' when Basil pointed at his crotch and 'tart' when he pointed at Sybil.
O'Reilly: If the Good Lord—
Basil: ...is mentioned once more I shall move you closer to him!
Doctor: Are you telling me you didn't realise this man was dead?
Basil: Well what was I supposed to think? I mean people don't talk that much in the morning! I was just delivering a tray! I mean, if the guest isn't up and singing "Oh What a Beautiful Morning" am I supposed to immediately think 'oh, there's another one snuffed it in the night?! Another name in the Fawlty Towers book of rememberance! I mean, this is a hotel, not the Burma Railway! It does actually say hotel outside, or perhaps I should be more specific! Hotel for people with a better than 50% chance of making it through the night! What?! What are you all looking at me like that for!
Sybill: Basil... you've got a kipper sticking out of your jumper.
Basil: Oh there it is! I've been looking for that!
Practically any scene with The Major is hilarious, but he has one line that's so jaw-droppingly offensive, and delivered with such panache you can't help but die laughing:
The Major: No, no, no, I said. niggers are the West Indians. These people are WOGS!
The fire drill from "The Germans" — while suffering from a severe case of "Funny Aneurysm" Moment after the real-life hotel burned to the ground — is still one of the best scenes in the series. It starts with Basil setting off the burglar alarm while getting the key to the fire alarm, thus forcing everyone to believe the drill has begun; this leads to a debate over the time the drill is supposed to be and what the bell sounds like. Then Manuel starts a fire in the kitchen, and everybody else — even Basil — assumes it's only the drill, even after Basil sees a smoldering Manuel emerge from the kitchen.
Also, Sybill's repeated phone calls to Basil while he's trying to put the moose's head up: "I was just doing it! I was just doing it you stupid woman! I just came over here to be reminded by you to do what I was already doing. I mean what is the bloody point of reminding me to do what I'm already doing, I'm doing it aren't I?"
"Would you like the hotel moved a bit to the left?"
"I wish it was an ingrowing tongue."
"WE'RE HAVING IT!!!!"
The Major repeatedly insisting there are burglars about.
Sybill: Did you put the lid back on the tank, Basil?
Basil: Yes, that's why I've been on the roof the last 20 minutes dear.
Sybill: And you took the pigeons out?
Basil: No I left them in, they're nearly done.
Basil: Go get me a hammer.
Manuel: Ah... hamma sandwich!
Basil: No, no a hammer!
Manuel: My... hamster?
Basil: No! How can I knock a nail in with your hamster? Well I could try...
Basil: Polly cannot cope!
Sybill: Well she can't fall over waiters or get herself jammed under desks or start burglar alarms or lock people in burning rooms or fire fire-extinguishers straight in her own face, but I should think the hotel could do without that sort of coping for a couple of days, what do you think Basil?
"No, no, I don't want a debate about it, Mr. O'Reilly. If you're not over here in 20 minutes with my door, I shall come down there and insert a large garden gnome in you. Good day."
And at the end of the episode, that's exactly what he leaves to do.
"And then I might go to Canada..."
The end of The Hotel Inspector.
"Good afternoon, gentlemen. And what can I do today for you three gentlemen? (Beat) AAAAH-!!!!"
Manuel: [Out of character, realizing he's flubbed his line] No, it's not a pigeon; it's a hamster.
[Sachs grins sheepishly, and Cleese — still in character — stares dumbstruck into the camera after hearing "Manuel" properly speak a full sentence in English]
Another blooper from "The Anniversary" has Sybil slamming the door in her husband's face so hard that the entire wall moves (if you watch the episode, they intentionally zoom the camera on Basil so the wall is out of shot). Cleese does a double take... and immediately begins "checking the joists".
Basil(to Sybil) I fought in the Korean War, you know. I killed four men.
Sybill: (to guests checking in) He was in the Catering Corps. He used to poison them.
Basil instructing Manuel over the phone to tell one of the builders: "You are a hideous orangutan."
That whole scene is just gold, Manuel trying to greet them, and keeps pronouncing the name wrong — "You men with Orraly!"
Worker(After another informs that he means O'Reilly): Yes, that's right. We are Orraly men! (under his breath) Thick as a plank...
When Sybil freaks out and attacks O'Reilly with an umbrella.
When Basil calls and says it's him, Manuel thinks he's someone asking to talk with Basil, and gets increasingly frustrated until he waves the phone around to demonstrate that Basil's not there. And then throws the phone over the counter in panic once he gets it.
Basil's inexplicable crouching, leaping performance after one mishap too many in "The Psychiatrist". * The psychiatrist walks past him with the immortal line "I'm on holiday..."
"It's perfectly Sybill! Simple's not well! She's lost her throat and her voice hurts. The doctor came this morning and said it was a bit serious, not a lot, a bit, she started to puff up, he's coming back later this afternoon and it's best for her to be on her own! Now what is so peculiar about that?" "Her driving around in the town."
"I'll just pop upstairs and ask her to stop dying, and you can all come up and identify her!"
"I'll call O'Riley, you go and see if the roof's still on." [...] *to O'Riley* "Oh, up to your usual standard I suppose, the odd hole in the floor, the odd door missing but nothing you can't be sued for!"
"Got to shoot him Fawlty!" "Ah not- not, legal actually, anymore Major. Murder."
*Basil kisses Sybill on the cheek to distract her: "What are you doing?" "I'm kissing you dear." *Sybill gives him a suspicious, confused look* "Well don't."
"You speak German?" "Oh, German! Oh, I'm sorry, I thought there was something wrong with you!"
The way Basil shakes his fist at the flower pot at the end of A Touch of Class is epically funny, every single time.
The running gag with the painting and Mr. Wareing who keeps trying to order his drinks coming together after the chaos is over. Fawlty, dejected that he's scared off his high class guests, finally tries to hang up Sybil's painting, only for Mr. Wareing to come in and loudly demand his drink. Basil snaps, smashes the picture on the floor, and frog-marches him back into the bar.
Mr. Hutchinson from "The Hotel Inspectors" asks Basil Fawlty if the hotel has a table tennis table - the reply is priceless (and was cited by John Cleese as a personal favorite line of his):
Basil: Indeed we do. It is not ... in absolutely mint condition. But it certainly could be used in an emergency.