What I would do, and this is just me, I would find a time that may seem appropriate. It could be months down the road. Maybe when they're having a sane day. But apologize.
Continue to show it in actions (like that's even possible at times) but speak the words later, much later if needed, when they might be in a frame of mind to accept it.
When they're in Monster mode, that is not the time to say it! I tried. I think it backfired and he used it as manipulation against me...seeing I was in a kinder and compassionate place, so he used that as a way to act like a friend and a great father but lie and sneak out of child support.
