The main problem with those people is their ego. They can't see someone being superior. So they never accept that they are wrong and you are right despite of the feeling of being wrong in the cold war. So if you stress on your logic to convince them, they blindly reject your logic. They don't even want to listen you clearly. That is why the first and foremost thing you should do is simply agree with him by saying "Yes, you are right."
When you surrender and listen them, they also feel that they should listen to you. When you start speaking, don't attack their argument directly. First support them and starts your point by saying "Yes, you are right. However I think......."
If they are listening to you, give strong logic. If possible manage some other friends to support you. If he finds more people supporting your logic, they will simply accept your logic and agree that you are the genius in that correspondence.
There are many ways to win verbal fight. The tips above are only some of them. You can use your own conscience to win such war in accordance with the situation and the type of people.
Discovered by +Don Prince