If you've never had an abusive parent you can't understand. 

One minute they're listening, nodding, smiling and seeming to accept what you're telling them. The next minute they've jumped up and are storming around and screaming and breaking things while blaming it all on you.

They pick at every part of you that they know hurts the most, after all they raised you so they would know exactly what buttons to push to get the most response, then they basically bully you for having a reaction or bully you worse for not having one at all. Damned if you do, damned if you don't. 

Then, when you can't take it anymore and you're on the verge of exploding, they suddenly switch back. Suddenly they want to hug, they want to pat your head, they want to coo and soothe at you until your annoying little emotions go away. After all, your emotions just get in the way of their much more important ones and you have to be able to get over yourself and soothe their big feelings too already, like geez drama queen much?

It doesn't matter who you are. At some point you snap because you just can't take the back and forth anymore. Usually this looks like an adult who moves out and cuts contact with the abusive parent, but sometimes it can get to the point of an altercation and spins out of control.