Oh, this is actually very easy to explain. I'll explain it from my point of view; not all NFs will agree with every single part of this.
NF often seek harmony in relationships. That doesn't mean they just want relationships to 'appear' harmonious or that they quickly dismiss their own needs so that things work well. They're actually invested in understanding other people and being understood themselves, deeply and profoundly. Genuine harmony is seen as one of the ultimate goals in a relationship.
On the road to understanding other people, there are often conflicts and arguments as you reconcile different opinions, needs, and interests. While other types tend to ignore certain levels of conflict, dismiss certain conflicts, or leave the relationship rather than explore the conflict, for NFs, it's really important to 'know' another human being for who they truly are, so they face the conflict.
Basically, we delve deeper into ourselves and other people instead of ignoring or minimizing aspects of ourselves that would cause conflict.
It may also be helpful for you to understand that for many NFs, relationships are the masterpieces of their life, somewhat like jobs or projects are the masterpieces for other types. We prioritize intrapersonal and interpersonal knowledge pretty highly, so it's less likely that we're quickly going to dismiss a conflict and spend our time doing something else (work, play, etc).
. I don't quite find anger in itself funny, but I see irony in many serious situations and have a laugh. I enjoy political incorrectness also.
