So, Today I had to pull the trigger, on my own "teammate".

I was in a match in squads with two friends, the 4th slot was a random we got filled in with. "He'll probably drop as soon as he can and die in the first minute" we all thought and agreed upon. We got surprised to see he waited to drop with us at loot-lake. We split off to different parts of the lake to maximize loot-grabbing and to pick off other squads dropping in after us. We kill 2 4-man squads wadding through the lake and start regrouping in the brick building on the edge of the lake. One of my friends and the random got in the building first and my friend finds and opens a chest, nothing useful aside from a shield potion. My friend grabs the potion and starts walking away, as he turns around the randoms starts spraying at him with his white AR. Apparently he wanted the potion. Myself and my other friend finally reach the door to the building after hearing the shots and the friend inside yelling that he was getting shot by the teammate. He ran out the door and closed it behind him. I crouched next to my friend right in front of the door and the now injured friend stayed behind us standing, forming a sort of fireing squad, all of us aiming shotguns at the door. The random opens the door, after dropping down the stairs, he stops dead in the door-frame, he didn't realize we we're all together and on comms. All 3 of us fired at the same time and downed him instantly. Noticing the storm closing in on us and knowing he had ammo we needed, I shot him in the back of the head, looted him, and ran.

Moral of the story, we need game-chat ASAP.

TLDR: random tried to TK because of shield potion, he got gunned down and looted because we couldn't talk it out.