I make an effort to mention this on every thread I see suggesting this: Team killing is not the answer. The act alone is labeled as toxicity, and isn't that something we all want to see less of in Siege? I get it, having someone on your team shooting friendly gadgets, teabagging everywhere, and not trying to win is an incredibly frustrating experience. I play this game as a normal player with friends or solo, so I experience these things too.
However, the best way to fight against griefers is to just ignore them and report their behavior in-game. Their sole purpose is to upset you and throw you off your game, so don't give them the satisfaction.