I'm an optimistic person on the whole, and usually, regardless of the argument, I'm over it in about five minutes, I just need a little breather. As a social and empathetic person, I'm also usually the one to cave and say sorry first.

But there's been a few times in my life when I just haven't been able to completely forgive the parties involved:

1. Way back in elementary school, we discovered my father was fatally allergic to cats. We had to get rid of the first pet to ever really be "mine", so we gave him to a "friend" from school who we knew would take care of him. I was easily bullied way back then, and so when she was feeling spiteful she'd tell me awful stuff that wasn't true, like that he'd lost an eye or gotten hit by a car. I used to cry and cry. Even that young, there's no excuse for that. She was a bitch raised by a bitch. I often wonder how she turned out.
2. For years and years, I hated, HATED my parents for moving me around two countries, four states and over eight cities. Now I'm over it... mostly. I see it helped me become a more diverse, well-rounded and open-minded person, but I still insist that it was absolutely the wrong time to start moving me: right at the onset of puberty and through my teenage angst years. I would have avoided a lot of the issues I had back then, I think, if I wasn't so insecure because we were always moving.
3. My middle school assistant principal, who decided that my grades and general lazy conduct weren't a sign that I was too intelligent for the classes I was in, and wasn't being challenged (I was also in Gifted and Talented at the time, and thriving), was me being a spoiled brat who would never amount to nothing, and she told me so in as much words. She also used the words "problem child", which cut deep and always have.
4. I'll probably get over this in a while, but it only happened last month, so it's still fresh and irritating. My English (college) class was having a discussion on perceived image and weight in American women, and as a busty, short woman myself, I shot off a few statistics about the "norm" changing: most women in America these days are a size 14. It's a fact, and I had evidence to back it up. She shot off VERY defensively (my immediate thought was she was sensitive because she had an eating disorder? I don't see why else she would be so sensitive on the 'skinny' side) about how women above size 8 were fat and lazy and weren't doing anything to help themselves. She said mothers shouldn't gain more than 20 pounds when pregnant, which is a COMPLETELY unrealistic and unhealthy statement, and I was the first one to call her out on all of it, taking MAJOR offense to just a boisterous claim. Many other women of all sizes in the class soon jumped in to defend my side as well. She hasn't shown up to school again since.