I would keep it there if I were you. It would only take them to be pissed at you taking control and report you. Far fetched it may seem sat on your computer pontificating but as an examiner I have seen how beligerant people can become when a skill test does not go there way. Put that personality into their own aircraft and you then seize control and you have a very dangerous situation developing.
Also as has been mentioned earlier, you take command and it goes pear shaped, rest assured the can will rest with you.
So as I said, I would leave it to the point where life and limb are threatened and you can defend your position to the hilt. I would also be reporting the incident immediately on landing.