First, the proviso that misuse to cause serious harm to others is rare and should not put anyone off using insulin to treat themsleves or their children...
But, there is a history of using insulin to cause death or harm - BBC news story here
http://news.bbc.co.uk/1/hi/health/6250172.stm about book "Insulin Murders - Real Life Crimes" written by Prof Vincent Marks and Caroline Richmond.