I can't stand when my shields are down after having a close call and winning a battle with one or two enemies and a teammate decides to toss a late grenade. I die and the enemy gets the credit. I want to toss the controller because it doesn't count as a
betrayal! I usually end up finding knob that tossed it and smack him upside the head the first chance i get.
If one of my teammates kills me on purpose, I will kick them. I will notice this if they are killing me repeatedly. If they just toss a grenade in the room and I happen to walk on the spot and get killed, it's my fault not theirs so I forgive them.