Can it be Epic Fail moments?
I'll leave it up to the other individuals involved if they want to out themselves.
Running through the final mission on Hard we managed to battle our way through all the queens and parasites and closed doors and rocks and so on and then, without spoiling anything, you have to get from Point A to Point B (a landing platform) within a certain timeframe.
By this stage most of the team was around half health and our medic either had only a few shots left of the medic gun or had run out entirely after having cured me of an infestation as we approached Point A.
So the timer comes up on screen and we leg it.
About 1/3 of the way there our Medic gets overwhelmed and gets gnawed to death.
2/3 of the way I was down to a sliver of health but managed to keep fighting while the other two kept legging it towards Point B. I eventually succumbed within sight of Point B... I may've made it but I went back to try and help our Tech who'd been trapped by aliens on the wrong side of a truck that was blocking our way.
I didn't make it. Shortly thereafter he didn't make it. Our Special Weapons guy made it to Point B but was being swarmed by aliens and died as the evac ship was almost there.
Cue much "Nooooooooooo!" and laughter as he dies.