You know a friendship is solid when you can argue about politics and still split fries after.

Disagreement is only dangerous to a relationship that was built on agreement. When two people know each other properly, an argument is just an argument, because the connection rests on something other than matching opinions. Being opposed and still comfortable afterwards is a decent measure of how real the thing is.

Let one disagreement run without steering it toward a conclusion. Say what you think plainly, hear the other side properly, and then eat. Being interested in why someone thinks differently is more useful than being right.