being hit by a house and an impromptu ice skating performance
Just a couple I can think of at the moment - Firstly when I was about 12 or 13 I was playing Mr Beaver (no jokes, please) in The Lion the Witch and The Wardrobe. Everything going swimmingly until one set change. I was standing on stage with the rest of my beaver family when the lights went down for a scene change - from forest glade to beaver house. Unfortunately I was stood about 1 foot too far forward and the entire house came crashing down from onto my head. A big thunk can be heard in the video of this, followed by the dim view of a shadowy pair of legs sticking out towards the audience. Luckily my chicken-wire constructed beaver hat saved me from concussion, but for the rest of the play Mr Beaver had a serious dent in his head.

Secondly, not acting this time but backstage for a play (name forgotten) I was suspended on a very wobbly and dodgy gantry swinging from the eves of the theatre in charge of the dry ice machine - I had to operate this at certain points during the play to provide a misty atmosphere. Nothing as strong as fog, you realise, just mist. For those of you who don't know, these machines are operated by lowering a basket full of frozen carbon dioxide into a container of water. The water melts the dry ice and the wonderful misty effects are produced. Dry ice is VERY VERY cold (about -80 centigrade) so wearing gloves is a must. After the second ambient misting, things were going fine. Until one of my gloves fell off into the dry ice machine. This blocked the vents completely and wedged the basket of dry ice into the machine. "Oh well," I thought, becoming increasingly enshrouded with smoke, "I've missed the cue for this one, but hopefully I'll be able to work the blockage loose for the next one."
Wrong. Very wrong.
Missed two more cues whilst trying to extract my glove. Eventually however, I worked the wedged glove loose, but at a completely inopportune moment. The machine belched forth its entire stored quantity of smoke all over the stage. Which at that time was set as a living room, and not a misty forest.
Bugger.
The amount of dryice and liquid that poured from above all over the stage hit the stage floor and turned into a layer of ice. Real ice, not dry ice. The play was immediately turned something that closely resembled 'muppets on ice' which although hugely more entertaining than the actual play, still earned me a bollocking.
(coderboi, Fri 2 Dec 2005, 12:45, Reply)