Saint's Row 2 - All of it.
Portal - All of it.
Disgaea - Ditto.
Smash Bros series - So many moments, all of them in the "you had to be there" category.
Armored Core 3: SL - In one particular match, I had been playing against a friend on the bridge stage. We were both using light mechs. Mine had a Karasawa and a blade, his had a blade and some back weapons. I managed to run out of ammo before he did, and was chasing him around under the bridge attempting to blade him when I decided it was time to drop the Karasawa. He happened to be coming up underneath me at the time, and tried to swing his blade at the exact moment I dropped my gun. Since the blade button is also used to pick up discarded weapons, he suddenly found himself holding a massive gun that his mech wasn't able to support, and the sudden weight killed his energy supply and caused him to plummet to his death before he realized what had happened.