The Pirates of the Caribbean attraction at both Disneyland and Walt Disney World features some pirates who are, quite frankly, drunk off their asses. You can even hear them butchering the theme song in places.
After Nick (miniaturized along with the audience) calls up to Diane that his pet python is now slithering loose, she passes out with a thud. Dr. Nigel Channing bends down into view to ask: "She didn't land on anyone, did she?"
The whole business with Adam picking up the auditorium to "show the little people to my mom!" And the very delicate process of putting it back exactly where it was before ("Otherwise the exits won't line up!"). Also a Great Moment for Disney Imagineering thanks to the wonderful swaying effect throughout, the work of a specially-rigged floor.
The punchline: Wayne gets the audience back to size, but in the process... "I blew up the dog!" The curtain closes on the chaos, but then Quark pokes through it and sneezes on the audience!
In It's Tough to Be a Bug!, Flik having to apologize for the termite's act going awry: "I hope none of you guys are allergic to acid..."
At the Royal Theatre, a comedic duo known as Mr. Smythe and Mr. Jones performs plays of Tangled and Beauty and the Beast with help from Rapunzel, Flynn, Belle, and Lumiere. Hilarity Ensues. For starters, Rapunzel refuses to let down her hair because it takes forever to braid, and Mr. Smythe assures Belle that Mr. Jones doesn't need any stage magic to act as dumb as Gaston.
Darth Vader Goes to Disneyland. The updated Star Tours hadn't opened yet, though, so Lord Vader and his Stormtroopers try to find ways to kill time until then, to the accompaniment of a twinkly remix of "The Imperial Theme".
Magic Kingdom (Walt Disney World)
When this troper and her friends did the Monsters, Inc. Laugh Floor, they weren't expecting huge laughs. It ended up being downright hysterical, mostly due to whoever they pick as "That Guy".
Footage of Roz saying, "The less you laugh, well, we might not have enough power to open the exit door." (forced laughter ensues)
The screens showing people who are seated with captions like "WILL TREAT EVERYONE TO CHURROS" and "HAS NO IDEA WHERE HE IS".
Epcot (Walt Disney World)
On the final ceremonial ride of Epcot's World of Motion (the predecessor to Test Track), the ride broke down. The GM executives on the ride had to walk to the exit.
Disney's Hollywood Studios (Walt Disney World)
The original Soundstage Tour had a segment demonstrating bluescreen techniques in which kids were picked from the crowd to ride the Honey, I Shrunk the Kids bee. After the finished scene is played back, the video reveals it's being critiqued by Siskel And Ebert, who give it a rave review — especially for the acting!
The original Magic of Disney Animation Tour's opening film, Back to Neverland, featured Robin Williams getting turned into a Disney animated character three years before Aladdin and put into the world of Peter Pan two years before Hook. When Tinkerbell sprinkles him and host Walter Cronkite with pixie dust, Robin comments "Ooooh, she's so bright...It's like being in the presence of Barbra Streisand!"
Superstar Television, which put audience volunteers in Chroma Key scenes of television then and now, had all sorts of funny moments, but the two best were probably:
The opening credits of Gunsmoke reveal a new cowboy hero: A baby on a rocking horse!
Neil Armstrong taking his one small step on the moon is marred by the accidental appearance of...the cue card holder, who flees for their life when they realize their mistake!
California Adventure (Disneyland Resort)
In Mater's Junkyard Jamboree, Mater himself gives the ride instructions before boarding. In English, they're hokey and fun. In Spanish, they become downright hysterical, thanks to Larry The Cable Guy's utter mangling of the Spanish language.
Hong Kong Disneyland
In the ride Big Grizzly Mountain Runaway Mine Cars you can see a bear scratching his back(which bears are known to do) against a lever which, depending on your personal and mental POV, is placed too low (down near his rear end) and looks like he's having a bit too much fun; there's also a father bear and his bear cub trying to cook salmon they caught — with dynamite.