Danger in this instance could mean many things, danger to self, danger to others and danger to both self and others as described in this blog post of mass-murderers who kill others before killing themselves: https://www.psychologytoday.com/blog/shadow-boxing/201503/danger-self-and-others
Danger can be defined in many ways though, the danger of suicide and self harm are fairly clear but danger could be over the longer term in terms of life style choices which increase risk of physical health problems or damage to one’s self esteem and psychological well-being.
These types of issues might be much more debatable, e.g. acts that may bring about the wrath of one’s community in certain cultures may put a person in danger, e.g. recent news stories about social media usage and selfie posting. Breaching social norms in some “tight cultures” could be an act, intentional or otherwise, that could put someone in danger and therefore arguably be considered abnormal due to its consequential risks.