When you are tired, you are very easily pissed off and can blurt out any stupid insult. You can't control it, even though you understand that it's a problem.

Today was one of those days. Nikto picked you up from work in a car. When you were driving along the road, your boyfriend started asking how your day was, etc. This pissed you off and you yelled at him. He immediately fell silent and continued to watch the road, but in silence. Now a silent bodyguard sits next to you.