Me and a friend managed to create an infinitely large fireball of despair.
A while back, when I was still into such things as 'Superbounces', firing weapons as the monitor, and that weird black triangle on Burial Mounds, I discovered a video explaining how to lose your arms in Halo 3.
Of course, I wanted to try out such a thing. Me and a friend proceeded to start a game on guardian, and in a few short minutes had the glitch working. As would be expected, this wasn't the preferred state of affairs for the game. As time went on, and we proceeded to kill ourselves in increasingly more unintelligent ways, forcing us to redo the glitch, the game became progressively more broken. We would occasionally disappear from existence, only to reappear minutes later. When we fired the splaser, it didn't fire from our body, seeing as we had no arms to hold it. Instead, it was brought down from the heavens in a blazing inferno to wherever we aimed. Later on, using the gravity hammer caused use to float in the air in a slow, drawn out arc a fair distance, sometimes moving in a full circle, before landing. We should have stopped when we could pick up weapons from across the map, but we pressed on, eager to see what vital function of the game would fail next. What did happen, caught us completely by surprise. My friend was standing off in the middle of the map as I proceeded to jump around without my left arm. In my infinite brilliance, I fell off of the map.
At this point, the game probably did one of two things; I'm still not entirely sure which. It had finally reached the final stage of breaking, and simply died right then and there, or it finally decided that shaking its case and saying "one more time..." simply wasn't working, and that if it did not in fact want us proceeding, it was time it took matters into its own hands.. Or case... Or something. Either way, at that point, the map simply exploded, and blamed it on me. Right at the moment my camera would normally switch over to a teammate while I waited to respawn, there was a bright yellow flash, and everybody died. Apparently I managed to pull a triple betrayal by merely dying. Besides the flash of light, which I managed to find by fast forwarding through a fair amount of video, it appears that the map simply became an explosion. There is no center, you can't see the edges, stuff didn't even get moved anywhere. My friend fell over, and the vehicles sat stationary, unharmed.
I still have no idea what happened, as there was plenty of other unexplainable stuff going on. In the end though, It was a very fun time, and it certainly made for a neat video.
Updated with a different video which explains the glitch
Update again: Apparently just yesterday, a friend found a way to recreate this! /not sure how yet.