Hmmm... I've seen many over the years. Some of the bigger ones:
-In WDW's Fantasmic, I'd camped out for 3 hours to get the front, center bench (the little short one). As the monkey barges came through, one of them drifted over... and smashed into the railing right in front of me! The monkeys were all thrown to the ground. To their credit, they all did the rest of the number form their knees. Then, in the same show, the Little Mermaid and Snow White barges were headed straight for each other. They narrowly missed, but in the course of swerving away, the Snow White barge got stuck on equipment near the stage. It was well into the Wicked Queen segment before they got offstage.
-At one of the 2002 Very Merry Christmas parties, I was working glow (carts with light up toys) in the Hub. When they went to start the fireworks, nothing happened. So they tried again, and this time two shells went off... then, nothing. It took them until about midnight to get the show going for real.
-In a showing of Celebrate the Season that same year, one of the toy soldiers turned walked face-first into the backdrop (between the stair cases) as they left at the end of the show. I even got that one on video. :lol:
-At one of the Aladdin showings at DCA, just before the One Jump Ahead segment started, the audio system went kaput. They brought the house lights back up, and had us wait. Well, the guy next to me (who had been very, very talkative all before the show) jumps up and yells "Let's do the wave!" So him, his girlfriend, and I got the whole Hyperion doing the wave while we waited. The show finally started back up, and at the part were Genie throws all the one-liners at Jafar, he paused, then asked, "Wanna do the wave?" :lol:
-In another Aladdin showing, Aladdin's wig started coming off in the middle of Friend Like Me, and he had to dance while holding it in place for the rest of the number.
-Yet another Aladdin one: while climbing up to get the lamp, I saw one Aladdin that slipped and got a face full of the stage!
-In DL's Fantasmic, during the Peter Pan segment, something went wrong with the Columbia, and a boat came rushing out after it. They grabbed onto the back of the ship and were messing with something, and went around with it all the way.
-I didn't see this one, but I definitely heard it across the park (and a performer who's a friend of mine explained it the next day): The pyro that sits out in front of the island in DL's Fantasmic all went off at once at the beginning of a show last month. The result was a huge boom, which I heard very clearly all the way from it's a small world!