"I'll bet you twenty bucks I can get you gambling before the end of the day!"
Even better in that he doesn't realize he's already won.
Lloyd's revenge on Harry.
"His head fell off?!"
Even funnier is Harry's follow-up, "Yeah, he was pretty old..."
Lloyd: That's it. I've had it with this dump! We got no food, we got no jobs, our pet's HEADS ARE FALLING OFF!!
When Lloyd accidentally goes the wrong way during the road trip:
"Huh. I expected the Rocky Mountains to be a little rockier than this."
"I was thinking the same thing. That John Denver's full of shit, man."
When Lloyd pulls up next to Harry on a Vespa, and explains that he sold the Shaggin' Wagon for it and gas money. Harry starts off sounding like he's berating Lloyd, saying "There are times I think you can't get any dumber! And then you do something like this..." Then he turns it on its head when he follows up with "...and totally redeem yourself!"
"It's okay! I'm a limo driver!"
"We landed on the moon!" Ad-libbed by Jim Carrey, to boot.
Harry introduces himself to Mary by saying "Nice set of hooters you got there" completely out of the blue. Although he makes a quick save by claiming that he's referring to the snow owls.
When Lloyd first suggests to Harry that they go to Aspen.
Lloyd: What are we doing here, Harry? We've gotta get out of this town!
Harry: Yeah, and go where? Where do you wanna go?
Lloyd: I'll tell you where: someplace warm. Where the beer flows like wine. Where beautiful women instinctively flock like the salmon of Capistrano. I'm talking about a little place called (whispers) Assspeeen.
Harry: I don't know, Lloyd; the French are assholes.
EEEAAAAAHHHH! HARRY! YOUR HANDS ARE FREEZING!
Also the Potty Humor where Harry just lets go and pees during the ride... the pair are frozen together by the time Lloyd stops.
"Dear Gas Man, packed up and drove to Aspen. Sorry about the $. Lloyd and Harry." *smiley face*
Even funnier since the villains think that Harry and Lloyd are criminal geniuses playing them for fools, taking "Gas Man" to be a reference to Mental's ulcer problems.
"Hey...you wanna hear the most annoying sound in the world?" Doubly funny if you watch Jeff Daniels start to lose his shit before the camera cuts to Mike Starr, also trying not to laugh.
At the bar while Lloyd is waiting for his supposed date with Mary, Beth shows up and starts rambling about her fake ex-boyfriend:
Beth: And I said: "Run, Beth, run for your life before this man kills you both." Then do you know what the klutz did?
The final scene in the movie was originally supposed to have Harry's line be the same, then Lloyd would actually get them on the bus with the bikini models. The finished ending is the result of Jim Carrey looking at the scene and going "Well yeah, but wouldn't thisbe even funnier?"