I just figured out this week that someone who kept insulting me on a specific area of my life was just jealous to and insecure about thst same thing in themselves. I think its probably reasonable to assume that insults reveal people's weaknesses and obsessive self doubt.

Like if someone didn't feel they were smart enough, they would be constantly assessing the intelligence of everyone around them and saying disparaging things to reassure themselves. I also noticed that a person in my family would keep pointing out that famous actresses were "fat" even though the actresses were all thinner than them. Whoever insults you are probably just trying to reassure themselves that they are good enough in some way.