The songs that vent about toxic people that you've cut out of your life? The lyrics that express how little you care for the ex, friend, parent, etc that screwed you over? Those songs hurt to sing. They hurt because...
You may be apathetic towards that person now, but you once cared so, so much... and look where it got you. Look how much your emotion towards that person was respected. It's a funeral march for what you loved and lost.
Never push a loyal person to the point where they don't care for you anymore.