Easy: remove yourself from the room.

If he can't give you the courtesy to let you finish, you need to implement your boundaries so people *do* show you the same respect they expect from you. 'You won't hear me out and let me finish? Okay then, bye'. If they actually want to have a conversation, then you come back.

It's not enough *telling* people to let you finish if they keep cutting you off. *Show* them that you mean business. No need for anger or blame, just calmly remove yourself.