That can be brutal. Two possibilities:
- You have just stumbled upon a "worthy opponent" which offers you the best opportunity for your academic life: a chance to master the skill of dialectic in a war for nothing less than your intellectual integrity. This requires building the skills of ruthlessness and patience. Take care not to let ruthlessness devolve into cruelty. And you'll have to master timing for it not to blow up in your face. Forewarning: this could take months. Time it for the end of the semester. :)
- Don't fight him in the slightest, but humor him. But do talk to your Deanthe Chair. Try to engage him/her on the problem since they are responsible for assisting you in exactly these issues by position of their office. If they can't help you, you can be sure that they don't deserve the office, because this is one of the most important issues for building the integrity of a university program and it is their job to help their faculty.