In my book Be a Duck! my first chapter talks about how we need to learn to let negativity go like water sliding off a duck's back. Holding onto hard feelings is only extra weight we will have to carry with us. It's not an easy thing to do, but it's necessary or pretty soon you will be so weighed down that you won't be able to move forward.
There is also an asumption that people make when they have a poor interaction with someone. And that is that it was personal. More often than not, when someone speaks harshly to you, it has more to do with what they are going thru than it does you. They may have just experienced something tragic and their emotions carried over to you. I'm not saying that it is justtified when that happens but rather it is understandable.