I've had a fair few lucky kills in Halo in my time, hail mary grenades and the like, but never anything like this...
Witness, as this player luckily manages hijack a Banshee, explode, refuse to leave the thing and then somehow skid out of control and kill a bunch of people in the opposing team. This has to be the luckiest kill streak ever.
It's not really any moment in particular -- the skid into the two enemies is classic, but it's everything that precedes it. I just love the way the player refuses to bail from the non-functioning vehicle and it somehow totally pays off.