Programmers have to work together as a team. When disagreement arises, it must be resolved somehow, it cannot be ducked for long. Difficult people are often extremely intelligent and have something very useful to say. It is critical that you listen to and understand the difficult person without prejudice caused by the person. A failure to communicate is often the basis of disagreement but it can sometimes be removed with great patience. Try to keep this communication cool and cordial, and don't accept any baits for greater conflict that may be offered. After a reasonable period of trying to understand, make a decision.