Some take on that character and personality to build a shell around themselves so they will be safer from attacks. Others do it simply out of a cruel nature. After they develop such a vicious mouth, few dare to challenge them. Others often join in and support or emulate them, giving added strength to their cruelty. They seem to compete in how many others they can embarrass or humiliate.
Adults suffer misery from verbal assaults from family, friends or co-workers.
Negative feedback distorts his view of himself. I don't mean to paint too bleak a picture. There are so many lovely, supportive people in the world who make life worthwhile for themselves and others. We hope to keep those rotten apples away from our children. Too many such days can damage a life.