I'm not going to stop arguing with my grandfather over the events that happened in the movie 'tombstone' because I know that I'm right about it.
Why do you care so much? Was this one of your favorite movies?
Yes, I'm a big fan of Westerns.
It doesn't really matter if you're correct or not about this, maybe instead of arguing over it you should watch the movie together?
I'm above that, I'm right and I don't care if I never see him again.
If you are both unwilling to see the other persons point of view and you don't want to watch the movie together, there may not be a point to argue. Talk to him and see if you have any other movies in common that you would like to watch together.