No doubt some rudeness and bullying comes from a place of insecurity. Other times, it comes from a place of superiority and need for dominance.
I used to “try to understand” too. The older I get, the less inclined I am to try to understand bad behavior. We all have a “right” to our feelings, but we don’t have the right to be rude or to bully people because of them. In the long run, we are responsible for what comes out of our mouths, and keeping them shut was always an option.