Rule number one. Never argue with someone whose opinion you don't respect.
Two, do not attack the other person.
Three, no name calling or discounting the other person's viewpoint.
Any Neanderthal can stoop to "fighting", it's more fun to make them look foolish by asking tough questions.

My wife and I always went by these rules. Sure, we split up but it was for other reasons, I still admire her mind.