One of the things that I occasionally have to deal with in the startups I work with is conflict, either between founders, or between employees. The most famous (infamous?) example was one founder to got mad at his co-founder because he claimed that the co-founder had rolled his eyes when the founder was talking.
As tempting as it might be to simply say, "Grow up, for goodness sake!" I find that it's better to offer more detailed and constructive feedback. To learn new techniques, I pillage the work of all kinds of conflict resolution specialists, including negotiators and yes, even marriage counselors.
(I feel compelled at this point to note that I've never been to a marriage counselor, nor has the need ever arisen. I just like to read widely.)
One of the key techniques of marriage counseling that you can steal for your startup is the use of XYZ statements:
"X represents a behavior; Y represents your feelings about it; Z represents a different behavior you would like to see. If, for example, you're angry about your husband not doing the dishes, an XYZ statement would look like this: "When you don't help me with the dishes (x), I feel disrespected and uncared for (y), and I would like for us to do the dishes together instead (z)"
The key to the XYZ statement is that it focuses on the specific and provides both an explanation and a suggestion for remedying the situation. It prevents things like catastrophizing, where leaving dirty socks in the bathroom becomes, "You're a dirty slob!" I've noticed that catastrophizing affects startups nearly as much as married couples.
When conflicts arise at your startup, try to have the combatants use XYZ statements. If they can't calm down enough to do so, paraphrase for them (something I end up having to do surprisingly frequently).