This has been suggested before, but it is not a feasible thing, that I know of. The reason for this is due to multiple scenarios where someone could be near each other but not teaming. Lets say you have someone crouched on the island somewhere, not visable to the other player. That player sticks around looting and what not, only to get detected as teaming and banned. There are also the cases where long fights occur and drag out. One player runs, the other chases, which then goes on for quite a while. It is much simpiler to have players record and report the teammers than it would be to code such a program. Especially since I am not sure it is possible due to those various scenarios where they are not teaming, but could be detected as such. Sorry, but it is not a good idea in my opinion.