Found the most scummy griefers yet.

4 chinese players, one green team and 3 in blue team. I was green team.

Green guy bought a humvee with an mg and went to pick up his 3 other friends from blue team and they just rode around killing our entire team.

The catch is that since the green guy is the driver, the humvee is marked as friendly on hud and on the map , and the driver knows exactly where the friendly players are, to just drive there and unsuspectingly mowing them all down.

Question. Why is it possible to be in the same vehicle as another team?

EDIT: One user in comments had a great idea to implement team kill assists, so that would be a great solution to fight this problem without the need to disable hoping in enemy vehicles entirely.