Whenever someone says Shaggy's keyword, be prepared to laugh.
Fred: Shaggy, what are you doing?
Shaggy: Saving your butt, Jones. Get used to it!
When Shaggy is in the middle of his awesome stunt to escape the mines, Daphne triggers the keyword that causes him to turn back into a coward. Eventually Fred motivates Shaggy enough to have him try to jump to the ledge he needs to get to, but he needs Fred to give him a movie line first.
Fred: ... How about, 'when you say jump, I say how high?'
Shaggy: Fred, that doesn't make any sense!
The G.P.S. from Abracadabra Doo makes the gang stop at a tattoo parlor.
The snarky owner of the buffet restaurant, who has a remarkably quick grasp on when things are going to get bad.
Owner:[after Shaggy and Scooby eat half the buffet in one sitting then go for seconds] So... do I file for bankruptcy now or...
And later, when the biker gang shows up.
Shaggy: Like, those guys aren't going to get out of control are they?
Owner: I think they'll be okay as long as no one does anything to aggravate them.
[Shaggy accidentally hits one of them in the face with his plate]
Owner: Like... that, for instance.
Lovestruck Velma. Especially the part where she spends an entire conversation with Winsor in such a monosyllabic lovestruck daze that he thinks she's not really listening at the end.
Velma and Winsor spend over a minute in a Held Gaze. Fred loudly clears his throat. Velma throws him a bottle of cough drops without taking her eyes off of Winsor at all.
Daphne's been riding a motorcycle since she was five. Complete with Cutaway Gag.
Fred: Isn't it illegal for a five year old to ride a motorcycle?
When the doctor finds out about Shaggy's condition, he forbids him to enter the Mystery Machine. So, Fred paints over some of the letters in yellow paint, and makes the Mustard Machine!
When Shaggy's trying to lead the gang out of the cave:
Svankmajor: ... Shaggy, you'd better hurry.
Shaggy: I was born hurried.
Fred: Is that part of the brave thing when you say weird stuff that sounds like movie lines?
Shaggy: Yes. Yes it is, big guy.
Fred: Well, alright then.
When Scooby-Doo finds a rare dinosaur bone, Professor Svankmajor thanks him and Shaggy for their significant contribution to Paleontology.
Shaggy: The study of pale things?
"This can go two ways, punk. One: you walk away. Two: I walk on your face."
"I've got a plan. On the count of three, you invent a time machine. One, two-"
*completely nonchalant* "Aaaaannd..." *sound of dribbling water* "theeerree goes the bladder..."
The point where Mr. Hubley gets out from his hiding place after the gang follows the raptors into town. He finds the food replicas that Scooby and Shaggy built of themselves, and thinks it's the real them.
Mr. Hubley: Scooby! Shazzy! No, they were so young!
"If there's on thing I can't stand, it's ghost dinosaurs!"