The film contains numerous references to other science fiction films, especially those of Steven Spielberg, as well as to general science fiction fandom. The story revolves around Paul, an alien who convinces two English science-fiction lovers to help him run away from the government agents who imprisoned him and planned to kill him.
- What do you know, the geek shall inherit the Earth.
- Sometimes you just gotta roll the dice.
- Over the last 60 years, the human race has been drip-fed images of my face, on lunchboxes and t-shirts and shit. It’s in case our species do meet, you don’t have a fucking spaz attack!
- Evolution, baby.
- Get your goddamn hands off my motherfucking junk!
- (to Graeme, who is drawing a portrait of him) Are you going to draw me like one of your French girls, Jack?
- You were amazing, Graeme! That cop didn’t suspect a thing! And Clive… you didn’t pee your pants.
- Yo, fucknuts! It’s probing time.
- Clive, I can feel your boner.
- Clive likes boning space bears!
Graeme Willy 
- He needs our help. Sometimes you just got to roll the dice.
- We’re just a couple of regular guys on a tour of the less touristy side of the American Midwest.
Clive Gollings 
- (in Klingon) Graeme. Strike this woman.
- Aliens aren’t called Paul.
- (after being asked about having sex with a girl dressed like an Ewok) Well, she was furry nice.
Agent Lorenzo Zoil 
- Motherfucking titty-sucking two-balled bitch!
- (after shooting the communicator) Boring conversation anyway.
- (to Haggard and O’Reilly) Listen to me, Frick and Fuck, I want you to tell me everything you remember about the pissy nerds.
- Three tits. That's awesome.
(sharing the same bed at the hotel)
- Clive: What are you going to dream about?
- Graeme: Wonder Woman.
- Clive: Please don’t.
- Graeme: (taking pictures of the Black Mailbox) Do you remember when we Googled it on your mum’s computer and the phone rang and you thought it was the FBI?
- Clive: I didn’t really think it was the FBI.
- Graeme: You started crying.
- Clive: I had jet lag.
- Graeme: We’d only been to Brussels.
- Clive: They’re going to rape us and break our arms!
- Graeme: I don’t want my arms broken!
- Graeme: Are you an alien?
- Paul: To you I am, yes.
- Graeme: Are you gonna probe us?
- Paul: (annoyed) Why does everyone always assume that? What am I doing? Am I harvesting farts? How much can I learn from an ass?
- Graeme: Uh – what?
- Paul: I’m Paul.
- Graeme: Paul?
- Paul: Yeah. It’s a nickname that stuck. My ship crashed on a… dog. It doesn’t matter!
- Haggard: (looking at the cover of Clive’s book) Ha! Three tits. That’s awesome.
- O’Reilly: You guys should have given her four tits.
- Graeme: ... That’s just sick.
(after Paul heals and eats a recently dead bird)
- Graeme: Did you ever do that to a person?
- Paul: Yes. I’ve eaten many people.
- (Clive looks at him, scared)
- Paul: I’m kidding, big guy. Relax.
(flashback of Paul talking to Steven Spielberg through the radio)
- Steven Spielberg: I want him to have some kind of special power. Something messianic.
- Paul: Okay, Steven, how about cellular revivification?
- Spielberg: Yeah, I don’t know what that is.
- Paul: Oh. Restoration of damaged tissue through telepathic manipulation of intrinsic field memory.
- Spielberg: What’s that mean?
- Paul: It means healing, Mr. Spielberg.
- Steven: Yeah, right. Healing!
- Graeme: (after Ruth fainted) If we take her with us, we could get her on our side!
- Clive: Yeah, you’d like getting her on your side, wouldn’t you?
- Paul: … That doesn’t make any sense.
- Graeme: There’s probably billions of intelligent civilizations out there.
- Ruth: So where is everybody? Hmm?
- Graeme: I - But one of them’s there! (points at Paul, who is in the RV showing them his butt)
- Paul: (to Clive) Are they looking? Are they looking?
- Graeme: Look, just because your truth isn’t the true truth, it doesn’t mean there’s no truth, Ruth.
- Ruth: That’s easy for you to say.
- Graeme: It’s really not.
- Ruth: Fuckeroo. That was the best titty-farting sleep I ever had.
- Paul: I have the feeling you’re new to cursing, Ruth.
- Ruth: (talking to the agents about Paul) He showed me things.
- O’Reilly: She’s talking about his spaceman balls! (Haggard slaps him)
(Paul becomes invisible in order for them to go outside)
- Ruth: Okay. I’m in.
- Paul: Rocky?
- Clive: Sure.
- Paul: Bullwinkle?
- Graeme: Well, I’m a little bit tired.
- Paul: Don’t be a pussy.
- Graeme: Don’t call me a – all right.
- Paul: (smoking a joint) It’s pretty strong shit, I got it from the military, actually. This is the stuff that killed Dylan.
- Graeme: Bob Dylan’s not dead.
- Paul: (smirks) Isn’t he?
- Zoil: I don’t want to be where you are.
- The Big Guy: Too bad, seeing as how I’m the one holding all the cards. And when I say "cards", I of course mean, big fucking gun.
- Paul: Very big gun.
- The Big Guy: Come on, Mork.
- Paul: Don’t call me Mork.
- [Graeme has just pushed Paul out of a rifle blast.]
- Graeme: That was close! [Pauses, looks down at the gaping wound in his chest] Oh my... [Collapses]
- Ruth: No!
- Clive: Oh God, Graeme! [Rushes to his side] Graeme!
- Mr Buggs: [Shocked] I never meant to...
- Zoil: Put the gun down, Mr Buggs!
- Ruth: Drop the fucking gun, Dad!
- Graeme: Oh no... I really liked this t-shirt...
- Clive: This is all my fault! We should never have come on holiday.
- Graeme: No, no, no, it's- it's fine, it's fine Clive, you know we've, we've had a good time, haven't we?
- Clive: Yeah? But you got shot.
- Graeme: Aghagh-- Yeah I know but, I can honestly say, Clive, this is the most fun I have ever had... [Dies]
- Simon Pegg as Graeme Willy
- Nick Frost as Clive Gollings
- Seth Rogen as Paul (voice)
- Kristen Wiig as Ruth Buggs
- Jason Bateman as Special Agent Lorenzo Zoil
- Bill Hader as Agent Haggard
- Joe Lo Truglio as Agent O'Reilly
- Jane Lynch as Pat Stevenson
- Sigourney Weaver as "The Big Guy"
- Blythe Danner as Tara Walton