One of my favorite stories that illustrate how to remain unaffected by other people's negativity comes from the teachings of the Buddha:
Make a Note
Buddha was walking through a village when an angry young man began insulting him. "You have no right teaching others," he said. "You are as stupid as everyone else. You are nothing but a fake." Buddha was not upset by these insults, instead he asked the young man, "Tell me, if you buy a gift for someone, and that person does not take it, to whom does the gift belong?" The man was surprised to be asked such a question and answered, "It would belong to me, because I bought the gift." The Buddha smiled and said, "That is correct. And it is exactly the same with your anger. If you become angry with me and I do not get insulted, then the anger falls back on you. You are then the only one who becomes unhappy, not me. All you have done is hurt yourself."
What this tells us is that ultimately, how we think, feel, and act is a personal choice. The challenge is when we don't get enough time to make a considered choice, such as being in the heat of an argument. The gap between stimulus and response isn't always long enough to choose the best response and we react emotionally, firing something back that we later regret, or say nothing and feel worse for not asserting ourselves in the moment. The topic of being assertive is vast and beyond the scope of this book; however, I would urge you to explore it as part of your ongoing personal development as a new manager.