Nothing Profound

I know that I no longer post regularily, so when I do, it would only make sense that I have something important to say, right?
Wrong.

I was just pondering something for a while that I wanted to jot down.
The reason I think that people come to dislike one another (from the best of friends to new lovers) is their own fault. When we meet someone, based on what they first say and how they first act, we automatically generate a first impression of them. Even if the whole time in our heads we're thinking, "that came out wrong, but I'm not going to hold it against them because they probably meant something less [insert slightly negative word here]," we're still unknowingly evaluating them to our subconscious standards. So, when these people do something that the mental patterns in our brains failed to predict (based on what [we thought] we knew about them), we get in a huff about how they're doing something "wrong". I don't think we're necessarily getting mad at them or what they did, we're getting mad at ourselves because we expected something else and we're redirecting that anger at them.
However, undoubtedly, some of the time what they do probably was offensive and conflicting with our own moral beliefs. But if this is true, how come it makes it okay for some of your friends to say those things and act that way and others cannot? Based on their background and experiences, you could be making mental exceptions, but what about those people that make you angry because they said something even though in retrospect, you realize it would have been fine if anyone else said it?
If anything, the only person in this note that I am referencing is myself (since I am the only person I can speak for); but it's just a thought.