A bad habit

As far as I am concerned, everyone has any bad habits at least one. Some have a habit of overusing alcoholic drinks or smoke, while some lie more often. Personally, I have couple of it but not like those I wrote above. I, for example, defend myself too much and think I am right, you're wrong etc., in any debate. I have noticed this habit for a long time, yet I am still unable to fix it. Let me give some incident, few days ago, approximately a week, my girlfriend and I were invited to my former house mate's house for dinner. Actually, we disliked the invitation because the host, the former house mate, had lied to us several times. She might be absent minded or neglectful or something like that. Sorry for too much detail of her. Let's move to the main point. For this reason, I phoned to my supervisor to ask for a day off. If the real reason had been told to the supervisor, she obviously would never have accepted. So I just lied saying that I had a headache and was unable to work that day-besides, told her I had never took a day off before. It was silly of me. I shouldn't have specified that. In response, she almost laughed and might have got I was lying. We had an argument on phone then no day off. At that time, what came to my mind first is that she is a bastard, not caring and I was absolutely right. I now understand I am not completely right. I need to fix it one way or another.