A bad fight is anything which does not help to move the relationship and the people involved forward. If one dominates the other, it will eventually be at the expense of the relationship. Everything depends on the intention. If the intention is to hurt, belittle, ignore, reject or win then good will struggle to come from that. If the intention is to wrestle with some boundaries and deal with unresolved issues then that is positive and important. Love for the other person and respect for their rights, as well as our own rights, will set a steady course for any argument. Of most value is a sincere desire to make the relationship work which, after all, is often why we fight. We want the relationship to honestly work.