In Halo: CE, on the fifth mission in the snow caynon, the last cut scene, you can kill MC and the cut scene would continue on with no one there. It's easiest in Co-op. You have to have a banshee or a ghost and good timing and/or aiming skills. Before you open the final door to the control room, position the banshee or ghost in the middle but back enough so you can get speed. In Co-op, have your partner open the door, and you can do one of two things. The first, you speed up and ram the banshee or ghost through the door, resulting in splattering MC. If you get enough speed, the banshee can reach the control panel and move Cortana a little bit. The second way, you need the banshee, position it in the middle, aiming down the middle. Your partner can open the door and you, at the last second, can release the banshee bomb, I call it, and instantly killing MC. You can also move Cortana this way but you would miss out on killing MC most likely.
Me and my friend were playing a little session of PvP when we were about the finish this level. I had the banshee and was planning on splattering my friend right before he opened the door. Only I missed him and the cut scene came and my banshee landed on MC. We, at the point, laughed for a total of 15 mins the first time. I was on the floor and my friend said to me, "You killed the MC. You're a traitor!" Those were the fun days...