Also known as an argument. Or worse, a fight.
My husband and I were there recently. We were both tired, there was too much left to do and we were not talking to each other. You know, when you get that sinking feeling that occurs before one of you blurts something out, something you probably wouldn't say if the circumstances were just slightly different (read: sane).
Couples are going to argue; the key is how you do it. I think we all mess it up at least some of the time. What's your strategy for such tenses times? Have a story that showcases your missteps? How about your triumphant ability to overcome little - or big - squabbles?