While it can be hard to not take things personally, especially with a difficult co-worker, it’s best to remember that others’ actions most likely have nothing to do with you.
In "The Four Agreements," Miguel Ruiz said, “When you are immune to the opinions and actions of others, you won’t be the victim of needless suffering.” In other words, allowing yourself to get upset over something your co-worker did is only going to hurt yourself, not them. Plus, taking things personally can make you feel like a victim, which can make you feel inferior and not the best version of yourself.