Our first people who we learn from are our parents as infants and toddlers.  Actions from our parents  teaches us what we can do.  Once we notice them yelling at or abusing people or damaging items, our actions often repeat.

Producers/Newscasters

Television and movies are likely the most common, accessible sources of entertainment we use in our lives.  Unfortunately, some of what we see, fact or fiction, are showing violent acts that shouldn't be sent for public viewing. http://www.calstatela.edu/faculty/sfischo/violence.html  http://www.cybercollege.com/violence.htm   http://www.ama-assn.org/ama/pub/article/1616-8841.html