They're easy to remember, but not so easy to avoid. Worth working on in any relationship, I think. They are criticism, defensiveness, ridicule and withdrawal. I wish I could figure out how to make that into a catchy acronym. It makes a lot of sense to me.
Criticism is corrosive.
It doesn't mean you can't give feedback and say how you feel. Or ask for what you want. Just do it nicely and don't put your partner down. And don't be defensive. Be open and willing to talk.