In my head, I always call this "the PAC exercise." The idea is that in any interaction between people, we tend to pick a role and speak and act consistent with that role. These are the three choices:
Parent: They are the seat of authority, the one with the power. As James Scott Bell puts it, the parent, "lays down the law. What he says goes. End of issue."
Adult: This is the most "objective" role. The rational and even-tempered one who can see things as they are.
Child: This person is not rational in the way they think. They tend to be selfish and want what they want, when they want it.
So, a conversation between two "Adults" is not going to be as conflict-ridden as a conversation between a "Parent" and a "Child." Or between two "Children." Or two "Parents." Ever been around two people who like to (and are used to) being the ones in charge, who are used to having the final say? Tension can mount quickly!
When you're thinking about your characters (or filling out character charts if you do that), consider what role they tend to take on when interacting with others.
Of course, most people would say they're "adults" because we all assume our way of thinking and doing things makes the most sense. It's also possible for characters to toward different roles depending on who they're with. Like because I spend so much time being a real-life parent to my real-life children, sometimes when my husband gets home, I tend to be a "parent" in our conversations as well. And I'm completely ignorant of it until he points it out to me.
The great thing about this exercise is that it can help you deepen your characters because you learn more about their inner workings. If they tend to be a "child," then what situations can push them into more of a "parent" role? Of if they're pretty level-headed, what makes their "parent" or "child" come out?
You can have a lot of fun with this one!